Anderson will undergo an MRI on Monday for further clarity on the injury and a timetable for return.
Making a start at power forward in place of LaMarcus Aldridge (rest), Kyle Anderson left late in the third quarter and did not return after going down with a noncontact knee injury.
The San Antonio Spurs said Anderson, 24, has a left medial knee sprain. Anderson underwent X-rays at the arena, a standard procedure, and they came back negative.
On a drive to the basket on which he was fouled, Anderson came down awkwardly and immediately grabbed at his knee. He stayed down for several minutes in obvious pain, pounding the floor with a closed fist at times. He was eventually helped off the floor and straight to the locker room by Aldridge and Manu Ginobili, unable to put any weight on his left leg.
It was a blow to the already short-handed Spurs, who have been without Kawhi Leonard all season and were sitting Tony Parker, Ginobili and Rudy Gay, along with Aldridge, on Sunday.
The Spurs stayed close, falling 90-87 after an open 3 from Brandon Paul with 8 seconds to play came up short.
Anderson, who has been starting in place of Leonard this season, was averaging 9.0 points, 6.1 rebounds and 3.0 assists in 22 games entering Sunday.