Klay Thompson could have re-entered the game for the Golden State Warriors, but he knew his work was done. It was Jan. 23, 2015, and Thompson had spent the third quarter scoring a record 37 points without missing a shot against the Sacramento Kings.

Early in the fourth quarter, after finishing with 52 points for the game, he grabbed a box score and a seat on the bench.

“He probably could’ve broken even more records,” James Michael McAdoo, one of Thompson’s former teammates, recalled in a telephone interview. “But it wasn’t even a thought for him: ‘Nah, man. I’m cool.’ And he treated the rest of the game like he would any other: always engaged, cheering for guys like me when I was getting those garbage minutes.”

At the time, the Warriors were just beginning to assert their dominance. They were still a few months from making the first of five straight appearances in the N.B.A. finals, a run that produced three championships. But while Warriors guard Stephen Curry was scripting drama on nearly a nightly basis, it was Thompson and his molten third quarter against the Kings that seemed to signal to the basketball-watching world that the Warriors — officially, undeniably — were different.

“It was ridiculous,” Bob Myers, the team’s general manager and president of basketball operations, said in a telephone interview. “Honestly, it’s a blur. That whole season, man, that’s the one where I should’ve just ridden off into the sunset. That’s the one where you’re saying to yourself, ‘Wow, this is a dream.’ Everything was perfect.”

Clips of that perfect quarter in that perfect season recently circulated on social media, marking the game’s sixth anniversary while offering a reminder of Thompson’s absence. It has been nearly 20 months since he last appeared in uniform for the Warriors, who have won 26 games without him.

After tearing up his left knee in the 2019 N.B.A. finals, Thompson experienced a calamitous setback in November, when he tore his right Achilles’ tendon in an off-season workout. All told, Thompson is expected to miss two full seasons. And in this strange, largely spectator-free period for the league, an endlessly drab atmosphere somehow feels just a bit gloomier because of his absence.

“It’s too bad for the league, for us, for everybody,” Myers said. “But mostly, for him.”

Thompson, who will turn 31 on Feb. 8, has yet to play a game since re-signing with the Warriors for five years and $190 million in July 2019. The psychological toll has weighed on him. Two seasons of his prime: gone. His teammates hurt for him, too. Curry told The Undefeated that he cried when he learned that Thompson had been injured again. “A lot of tears,” Curry said.

The jarring part, McAdoo said, was that Thompson had seemed fairly indestructible, rarely missing games through his first eight seasons.

“I don’t think I ever even saw him getting therapy,” said McAdoo, who spent three seasons with the Warriors, from 2014 to 2017, and now plays in Japan. “Dude was a tank.”

McAdoo, though, recalled how Coach Steve Kerr would often say that teams needed to be good, and they also needed to be lucky. Thompson is coping with his share of bad fortune.

“He has faith that he’s going to come back 100 percent,” his father, Mychal Thompson, said in an interview. “He knows he needs to be patient.”

Mychal Thompson, a former N.B.A. center, added that his son had been encouraged by the high-level play of the Houston Rockets’ John Wall and the Nets’ Kevin Durant, both of whom missed significant time because of Achilles’ tendon injuries before returning this season. The Warriors are planning/hoping/yearning for Thompson’s return before the start of next season.

On Saturday night, Thompson made his first public comments of the season when he joined the NBC Bay Area’s broadcast crew for a stretch of the Warriors’ 118-91 win over the Detroit Pistons.

“Just a little bored at times,” Thompson said. “But I’m feeling good. I’m happy to be back with my teammates. Unfortunately, I’m not playing. It kills me every day, but I plan on playing for a long time, and I don’t want to have any mishaps come this rehab.”

Thompson, who remains in a walking boot, added that he had been reluctant to make his cameo, but then he saw that the network had produced a branded “Reporter Klay” backdrop for him to use.

“Someone went through great lengths to make that happen,” he said, deadpan, “so I felt bad not fulfilling my end of the deal.”

Myers likened his job as general manager to assembling a jigsaw puzzle: Say the puzzle is missing a random piece toward the right. Though the missing piece might be noticeable, Myers said, the general idea of the puzzle would still be intact.

Now say the puzzle is missing one of the corners.

“If you walked into the room and looked at it, you’d say, ‘Where’s the corner piece?’” Myers said. “And I’d say, ‘Well, I can’t find it.’ And you’d say, ‘Well, the puzzle looks screwed up.’ And I’d say, ‘It didn’t come in the box!’ But I know it stands out. Klay is a corner piece.”

The Warriors were missing two corner pieces last season. Curry was sidelined for all but five games because of a broken left hand. Thompson split his time between San Francisco and Los Angeles as he focused on rehabilitating his knee. He watched from a remove as the Warriors finished with the worst record in the league.

“It’s pretty abrupt to go from five straight finals to just out for the season,” Myers said, “and I think he was just working through how to manage that mentally. I can’t speak for him, but I think he was trying to figure out where to be, and it was challenging.”

This season, Curry has returned to his familiar form, and the Warriors — with multiple new pieces — have been mostly competitive after a rocky start. At the same time, Thompson has been a much more consistent presence around the team, taking up residence on the bench at home games — something he did far less often last season.

“I think it’s much better for him to be around the guys and feel like you’re a part of it,” Mychal Thompson said. “It helps the time go by faster.”

Klay has picked his spots to counsel teammates, like the first-year center James Wiseman, who received several tips from Thompson during a recent game against the Minnesota Timberwolves: Stay aggressive, take care of your body and be a great teammate.

“I just love to listen,” Wiseman said in a conference call, “and he can tell.”

Thompson has long kept his approach simple. He loves his dog, a bulldog named Rocco, spending time by the water, playing chess and shooting a basketball. His demeanor has not changed since he entered the league in 2011, which is no small feat. He is as popular among his peers as he is with fans. Few players, if any, are less polarizing.

“I think what’s most endearing about Klay is that what you see is what you get,” Myers said. “And that is so hard in the N.B.A. It’s such a hard place to not be affected by the money, by the celebrity, by social media, by the fans — who the heck knows? But he’s always put himself and the N.B.A. in the proper place. He’s maintained his center.”

The public got a quirky glimpse of that in 2017, and it had nothing to do with his 3-point shooting or his defensive prowess. The Warriors were in New York to play the Nets when Thompson was randomly stopped on the street by a television news reporter who was interviewing people about the dangers of faulty scaffolding. Thompson proceeded to do an on-camera interview in which he explained his mental calculation about whether he walks under scaffolding or around it.

“I usually observe if the piping and stuff is new,” he said.

When Thompson was later asked about his cameo on the local news, he told reporters that he had wanted to offer his thoughts as a “concerned citizen.”

“There are a lot of layers to Klay,” Myers said, “and all of them are good. When you peel them back, you just get more authenticity with him.”

McAdoo said he was always struck by Thompson’s pregame ritual of reading the newspaper at his locker. (Thompson has said that it helps him relax.)

“And he actually reads it,” McAdoo said. “I just found it so odd: ‘Bro, who still reads the newspaper?’”

Myers daydreams about Thompson’s eventual return, he said, and about what it will mean for Thompson and for his teammates. In the meantime, another season lurches along without him. The wait continues.