Cardinals manager Mike Matheny said Molina, who is getting his first rest in four games, has played through the pain the past few days.
"He rolled it two days ago, and it seemed to tighten up and swell on him [Friday]," Matheny said. "He's just been pushing through."
Molina put the Cardinals ahead with his solo home run in the sixth inning of Friday night's 8-5 win as part of his 3-for-5 outing.
When asked if Molina would be out for an extended period of time, Matheny said the club was basically taking it day by day.
"We don't know," he said.