Bregman was injured in the first inning of a win against Texas on Wednesday night while running to first base when he grounded into a double play. He pulled up a few steps before the base and hobbled off the field before heading to the clubhouse.
Astros manager Dusty Baker said there isn't currently a timetable for his return.
"We really don't know," Baker said. "He's being evaluated by doctors today. Even when they do tell us, to tell you how long it's going to be, it's merely a guess."
Bregman is hitting .275 with seven homers and 34 RBIs this season.
Catcher Garrett Stubbs was recalled from Triple-A Sugar Land to take his spot on the roster.