The Nets’ first loss of the season Sunday night at Charlotte has proved especially costly, with the team announcing on Monday that Spencer Dinwiddie, who has been starting at guard alongside Kyrie Irving, partially tore the anterior cruciate ligament in his right knee and is out indefinitely.

Early in the second half of the Nets’ 106-104 loss to the Hornets, Dinwiddie fell to the floor clutching his right knee after an awkward step in the paint as he passed the ball to Kevin Durant. The team said more details about Dinwiddie’s recovery are expected after surgery next week.

Dinwiddie averaged 6.7 points, 4.3 rebounds and 3.0 assists in 21.4 minutes per game in the Nets’ 2-1 start. The Nets routed Golden State at home and Boston on the road in its first two games before slumping to defeat against the Hornets, who had started 0-2 and are not expected to contend for the playoffs in the Eastern Conference. The Nets will be without Dinwiddie, Durant and Irving on Monday night against Memphis at Barclays Center, with Durant and Irving being held out for rest on the second night of a back-to-back.

Dinwiddie, 27, averaged 20.6 points and 6.8 assists per game last year while Durant was sidelined for the entire season while recovering from an Achilles’ tendon tear and with Irving limited to just 20 games by various injuries. But Dinwiddie did not join the Nets in the bubble at Walt Disney World near Orlando, Fla., in July, missing the N.B.A. restart while recovering from Covid-19.

He earned a spot in the starting lineup this season when the new Nets coach, Steve Nash, decided to deploy Caris LeVert as a sixth man, only to be felled by the second knee injury of his career. Dinwiddie tore the anterior cruciate ligament in his left knee during his junior season at Colorado.

The injury Sunday occurred on a drive to the basket against Charlotte’s Bismack Biyombo. Dinwiddie hobbled to the Nets’ bench and, after some treatment, was soon ruled out of the game for what was initially termed a right knee sprain.

“When Spencer is going, he can’t be stopped — his offensive game when he’s going downhill creating shots for others,” Jarrett Allen, Dinwiddie’s teammate, told reporters after the game. “And even off the court, everyone loves having Spencer around. His energy, just his personality, is great in the locker room.”

Playing on what is regarded as one of the N.B.A.’s most attractive contracts, Dinwiddie can become a free agent at season’s end or invoke a $12.3 million player option for the 2021-22 season.

Despite Nash’s lack of coaching experience and uncertainty about how Durant and Irving would mesh after injuries prevented them from playing together in their first season in Brooklyn, the Nets are widely billed as a championship contender — in part because they have one of the league’s deepest rosters.