He will be reevaluated before Friday's game against the Phoenix Suns, and is a game-time decision.
Celtics coach Doc Rivers said after Thursday's 88-78 win over the Portland Trail Blazers that Pierce, who finished with 17 points, made contact with a Portland player. And although he didn't believe it was serious, Rivers did note that Boston didn't need any more injuries.
"We'll just wait and see," Rivers told reporters. "I don't know if he'll get X-rays . . . We'll find out [Friday].
"I think he bumped knees [with a Portland player]. We're hoping it's nothing more than that."
Pierce, who departed Tuesday's game against the Cleveland Cavaliers early to get treatment on what he dubbed a "tweaked" ankle, hobbled off the court with 2:01 to play Thursday and went right to the locker room.
Pierce limped to the bus but told reporters he will wait to see if the injury swells overnight before deciding if he can go against the Suns.
Chris Forsberg covers the Celtics for ESPNBoston.com.