Walker suffered the injury in the bottom of the third inning when he came up lame running to first base after laying down a bunt.
The Mets didn't have an update on Walker's status after the game, but he is scheduled to undergo an MRI on Thursday.
"I'm concerned," manager Terry Collins told reporters after the Mets' 9-4 win, according to Newsday's Laura Albanese.
Entering Wednesday night, Walker was slashing .271/.353/.471 with nine home runs and 33 RBI—which is already 60 percent of last season's total.
Should he miss significant time, the Mets will have to shuffle their infield around a bit.
Third baseman Wilmer Flores could be a candidate to slide over to second in Walker's absence, but the Mets could also opt to plug in T.J. Rivera—who was recalled from Triple-A Las Vegas on Tuesday.