Millsap, who had 12 points and seven rebounds Saturday night, went to the locker room with 4:48 remaining in the quarter. He was diagnosed with a strained left patella tendon.
The power forward had left earlier in the period to get a brace refitted, but just more than a minute later he signaled to the bench that he couldn't continue.
Millsap averages 17.2 points and 7.9 rebounds per game. He has been slowed by several nagging injuries, including a sprained thumb.