Asked about Lee's status after Game 3 of the Western Conference finals, Spurs coach Gregg Popovich said: "I have no idea."
Lee injured the knee with 2:57 remaining in the first quarter after he scored on a layup contested by Draymond Green.
Lee was fouled on the play, but he wasn't able to take the ensuing free throw attempt because of the injury.
Lee winced in pain immediately upon landing, and he was down on the floor near the tunnel leading out toward the locker rooms. Athletic trainers helped Lee to his feet. He hobbled toward the locker room before trainers took over and rushed him down the hall in a wheelchair.
Joel Anthony replaced Lee in the game.
The Spurs later said Lee would not return to the game. By rule, because he was unable to attempt the free throw, he would not have been allowed to return even if he were healthy.
Lee is the club's third player to suffer an injury significant enough to take him out of action. San Antonio already was without star forward Kawhi Leonard, whom Popovich held out because of a sprained left ankle. That injury occurred after the club already had lost Tony Parker in the Western Conference semifinals because of a ruptured quadriceps tendon.
The Warriors lead the West finals 3-0.