A coronavirus outbreak across the league has cast a shadow over Saturday’s highlight slate of games, with several key players unavailable to compete.The N.B.A. has long looked to Christmas Day as a highlight of the young season, a made-for-TV spectacle that brings together many of the best teams and best players for a daylong extravaganza of basketball fireworks.This year? Not exactly.Dozens of players have been cycling through the N.B.A.’s coronavirus health and safety protocols in recent days, forcing teams to improvise by signing scores of replacement players to 10-day contracts. So if you’re expecting to see Kevin Durant lead the Nets into their game against the Los Angeles Lakers on Saturday, you’ll be disappointed: On Friday, Durant remained in the protocols. But fans should be able to catch the surprise return of Joe Johnson, whom the Boston Celtics signed on Wednesday to shore up their own battered roster — the same Joe Johnson who is now 40 and had last appeared on an N.B.A. court in 2018.The pandemic has wrought havoc on the holiday season, and the N.B.A. has not been immune. The league even issued a memo this week to the teams scheduled to play on Saturday that their tip times could be tweaked if any of the prime-time games are postponed. (The Nets, for example, have already had three games scuttled over the past week because of low roster numbers.)For now, and keep in mind that this is subject to change, here is a look at the five games penciled in for Saturday:All times Eastern.Atlanta Hawks (15-16) at Knicks (14-18), Noon, ESPNKnicks forward Julius Randle is having an up-and-down season, but his short-handed team will need him against the Hawks on Saturday.Mary Altaffer/Associated PressSurprising runs to the playoffs last season led to these teams meeting in the first round, spurring talk about the two franchises resurrecting. The Hawks easily dispatched the Knicks then, with the Hawks’ star player, Trae Young, delighting in quieting abrasive Knicks fans, while the Knicks’ top player, Julius Randle, had a terrible series.The matchup looked like it would start a rivalry between two up-and-coming teams on their way to the Eastern Conference’s elite.But this season, both teams, far from being resurrected, have been two of the more disappointing teams in the league. The Knicks’ new additions, Evan Fournier and Kemba Walker, have been mostly underwhelming, though Walker, after being benched for several games, has been on a tear in a recent return to the lineup. And while Atlanta had one of the N.B.A.’s worst defenses, its stellar offense hasn’t been enough to compensate for it. Young, already one of the league’s best offensive players, is having the best year of his career, while Randle has struggled.The good news is that the same thing happened last season, and both teams had impressive second half turnarounds to make the playoffs.The Christmas game will undoubtedly lose some of its luster with several key players likely to miss the game as a result of the N.B.A.’s health and protocols, including Young, Clint Capela and Danilo Gallinari from Atlanta, and Nerlens Noel from the Knicks. Derrick Rose, one of the Knicks’ lone bright spots against Atlanta in the playoffs, is slated to miss several weeks with an ankle injury.Boston Celtics (16-16) at Milwaukee Bucks (21-13), 2:30 p.m., ABCJayson Tatum’s shooting percentage is down slightly this season, but he is still Boston’s leading scorer with 25.6 points per game.Charles Krupa/Associated PressFresh off their first N.B.A. championship since 1971, the Bucks knew the early part of their schedule would pose some challenges. For starters, last season’s playoff run extended into late July. Then, two of the team’s best players, Khris Middleton and Jrue Holiday, helped the United States men’s basketball team win gold at the Tokyo Olympics in August. The Bucks subsequently reconvened for the start of their season and lost eight of their first 15 games.Despite a shifting roster — Middleton and Giannis Antetokounmpo are among the players who have missed games after landing in the league’s health and safety protocols — the Bucks seem to be finding their footing as they eye another title. That’s no great stretch, thanks to the presence of Antetokounmpo, a two-time winner of the Most Valuable Player Award who still seems determined to expand his game. He is expected to play on Christmas after missing the past five games.The Celtics, meanwhile, are enduring growing pains under Ime Udoka, their first-year coach. From the start of training camp, Udoka has stressed the need for his players to pass more willingly around the perimeter. But too often, the ball still sticks — frequently in the hands of Jayson Tatum, a talented young player who has struggled with his shooting this season. The Celtics have also been hindered by injuries to Jaylen Brown.Boston needs to play a much more complete brand of basketball to have a shot of landing in the postseason, let alone to challenge the likes of the Bucks.Golden State Warriors (26-6) at Phoenix Suns (26-5), 5 p.m., ABCChris Paul leads the league in assists per game, which has helped his Phoenix Suns stay among the West’s best despite injuries.Ezra Shaw/Getty ImagesThis game features the top two teams in the Western Conference. The Suns are hoping to improve upon their trip to the finals last year, while Golden State looks to continue its resurgence.In November, the N.B.A. began investigating Robert Sarver, the Suns’ owner, after ESPN published accusations of racism and sexism against him from what ESPN said were current and former Suns employees. If the specter of that investigation has affected the team, it hasn’t shown on the court.Phoenix has looked formidable in Coach Monty Williams’ third year with the franchise. After a 1-3 start to the season, the Suns went on an 18-game winning streak, which set a franchise record for consecutive wins. That included a win over Golden State and ended with a loss to Golden State. Aided by point guard Chris Paul’s steady veteran hand (he leads the league in assists per game), they’ve weathered injuries. Deandre Ayton missed eight games with a leg injury and illness, and Devin Booker missed seven games with a hamstring injury.Golden State awaits the return of Klay Thompson, Stephen Curry’s sharpshooting counterpart, who has been absent for more than two years with two serious injuries. He could return soon, but not in time for this game. The team has rocketed to the top of the conference even without him.Curry set the N.B.A. record for career 3s last week and has been playing well enough to merit consideration for his third M.V.P. Award. Role players, such as Jordan Poole and Gary Payton II, have made major contributions as well.Nets (21-9) at Los Angeles Lakers (16-17), 8 p.m., ABC and ESPNThe Nets have been hit hard by the virus recently, with so many players, including James Harden, unavailable that three games were postponed.Carmen Mandato/Getty ImagesIdeally, this would be a matchup of the Nets’ Kevin Durant against his longtime elite contemporary, LeBron James of the Lakers. And in theory, there would be other stars, too, like Kyrie Irving for the Nets and Anthony Davis for the Lakers.But it’s not to be. Davis is out for several weeks because of a knee injury. And the Nets are missing so many players as a result of the league’s health and safety protocols — including Durant and Irving — that their last three games have been postponed. On Thursday, Nets Coach Steve Nash announced that James Harden had left protocols, making him available against the Lakers.For this matchup, the Nets, who are in first place in the Eastern Conference, are taking on a Lakers team fighting just to stay in the conversation to make the playoffs.The Lakers’ supporting cast around James and Davis, thus far, has proved to be ill-fitting, and the roster has dealt with a scourge of injuries. Russell Westbrook, the Lakers’ most high-profile off-season addition, has struggled at times. James is putting up exceptional numbers for a 36-year-old, but appears to be finally slowing down: He’s more reliant on his jumper than ever before, averaging a career high in 3-point attempts per game, and a career low in free-throw attempts per game. James is still one of the best players in the league, but it’s not apparent that he can carry an offense by himself like he used to.With the Nets slated to be without so many key players, this should have been marked as an easy win for a James-led team. But not this year. These Lakers, even at full strength, are mediocre and prone to coast through games. Right now, it’s a tossup.Dallas Mavericks (15-16) at Utah Jazz (22-9), 10:30 p.m., ESPNDonovan Mitchell, left, and the Utah Jazz will face a Mavericks team that has been dealing with injuries all season.Rick Bowmer/Associated PressWhat’s regular-season dominance without playoff success? The Utah Jazz found themselves confronting that question last season when they finished the regular season with the best record in the N.B.A., but only reached the second round of the playoffs.That’s meant so far this season their game-to-game focus is on not just their early wins and losses, but on what lessons they can take into the postseason.“If you’re perfect in November, no one’s going to care come playoff time,” Jazz guard Donovan Mitchell said.Mitchell has led the Jazz offense with more than 25 points per game, while Bojan Bogdanovic and Jordan Clarkson, the league’s reigning sixth man of the year, have also been important pieces.Defensively they are led by Rudy Gobert, who is the league’s best with 15.1 rebounds per game and also contributes more than 2 blocks per game.They’ll face a Mavericks team that has dealt with injuries all season, including to guard Luka Doncic, their best player, who is expected to miss this game because of the league’s health protocols.Although Doncic leads the team with 25.6 points per game, the Mavericks are not dramatically different statistically when he’s on the court. But they are more fun to watch. If Doncic misses the Christmas Day game, a Dallas team ravaged by the virus and injuries will have a tough time making a game against the Jazz interesting. More