Tom Haudricourt of the Milwaukee Journal Sentinel reported Braun will be placed on the disabled list.
Jesus Aguilar pinch hit for Braun in the bottom of the fourth inning. He was not involved in any defensive plays in the top of the fourth but has had a lingering calf issue for most of May.
This was only the sixth time Braun has been in the lineup this month, and he did not play in Wednesday's loss to the Toronto Blue Jays. Braun also dealt with injuries to his forearm and trapezius earlier in the month.
Sunday's loss to the Chicago Cubs was the first time he'd played since going on the disabled list May 12. The Brewers went 10-5 with Braun out of the lineup this month and are currently 25-21, sitting first in the NL Central.
Having the calf as a lingering problem isn't going to do much to help him break out of a slowish start. Braun is hitting .265/.353/.529 with seven home runs and 19 runs batted in this season.