Harrison was removed from Wednesday's game against Pittsburgh due to cramping in both of his calves, Todd Rosiak of the Milwaukee Journal Sentinel reports.
The Pirates selected Simon's contract from Triple-A Indianapolis on Wednesday.
Pittsburgh reinstated Sisk (elbow) from the 15-day injured list Wednesday.
May is expected to make his Brewers debut against the Pirates on Thursday, Sophia Minnaert of Brewers.tv reports.
Bauers (abdomen) is not in the Brewers' starting lineup against the Pirates on Wednesday, Hunter Baumgardt of Fox Sports 920 Milwaukee reports.
Horwitz is not in the Pirates' starting lineup against the Brewers on Wednesday.
The Brewers reinstated Harrison (forearm) from the 15-day injured list ahead of his scheduled start Wednesday versus the Pirates in Milwaukee.
Milwaukee optioned Anderson to Triple-A Nashville on Wednesday, per Hunter Baumgardt of Fox Sports 920 Milwaukee.
The Pirates reinstated Devenski (illness) from the 60-day injured list Wednesday and outrighted him to Triple-A Indianapolis.
Pittsburgh reinstated Sisk (elbow) from the 15-day injured list Wednesday.
