Wainwright was put in a walking boot and manager Mike Matheny said the clubhouse was "pretty somber" after a 5-3 win over the Milwaukee Brewers.
"Well, we won't know for sure anything until we get a picture on Monday. But, it's in the back of his ankle and that's a bad spot," Matheny said.
The Cardinals said Wainwright will be re-evaluated back in St. Louis after the team's road trip ends Sunday.
Wainwright had a 2-0 lead when he stumbled getting out of the batter's box on his popup that led off the fifth inning. He was helped off the field by a trainer and left the game.
"My foot just shut down on me," Wainwright said.
