The Brewers placed Harrison on the 15-day injured list Saturday, retroactive to Thursday, with left forearm tightness, Curt Hogg of the Milwaukee Journal Sentinel reports.
Harrison made an early exit from his last start due to an injury, and although he said after the game that he wasn't too concerned about it, the Brewers will move him to the injured list anyway. Robert Gasser will come up from the minors to fill the open roster spot and figures to claim Harrison's place in the rotation until further notice.