Lillard underwent an MRI after the game, the results of which were inconclusive, the Blazers said. Lillard is scheduled to undergo a second MRI on Tuesday.
He finished with 11 points on 3-of-9 shooting in 27 minutes. He appeared to injure the knee on a drive to the hoop on which he planted his right foot and grimaced in pain.
Walking gingerly on his right leg, Lillard went to the locker room. He returned to the court for a few possessions and went back to the locker room again with 5:18 remaining in the quarter.
Lillard, whose scoring helped carry the Trail Blazers out of the seeding round and into the playoffs, suffered a dislocated left index finger in Game 2 of this Western Conference first-round series.
Game 5 is slated for Wednesday in Lake Buena Vista, Florida. The Lakers lead the series 3-1, and now the question is whether Lillard will be active for a potential elimination game.