Mitchell was injured Tuesday night after a head-first evasive slide into second base in the 10th inning. He remained in the game but was removed in the bottom of the 10th after a throw to home plate.
Brewers manager Craig Counsell originally called it a right shoulder injury.
Mitchell had come back to earth after going 4-for-10 with three home runs -- including a walk-off -- against the New York Mets in the Brewers' second series of the season. He hasn't homered since and is batting .259 with six RBIs.
Perkins, 26, is batting .292 with a homer and three RBIs in 13 games at Triple-A Nashville. He has yet to make an appearance in a major league game.