Parker limped off the court with 5:09 left in the third quarter after he appeared to bang his leg against Ryan Hollins' knee. He finished with eight points and six assists in 26 minutes.
Coach Gregg Popovich said Parker was having trouble walking on his right leg and that was why he didn't return to the game. Asked whether Parker was day to day, Popovich said, "I don't know; it just happened a few minutes ago."
Parker didn't speak with reporters after the game. However, teammate Manu Ginobili lamented his exit.
"He has the ball in his hands for a long time, especially when it counts the most," Ginobili said. "So we couldn't adjust to it and it was hard, especially against a team that is aggressive."
Parker is averaging 18 points, 6.0 assists and 2.6 rebounds in 30.4 minutes per game. The Spurs, whose 19-5 record is third-best in the NBA, next play Wednesday in Phoenix against the Suns.
The Associated Press contributed to this report.