Mench, acquired in July 2006 from Texas in the Carlos Lee trade, batted .267 in 101 games for the Brewers last season, adding eight homers and 37 RBIs.
The Brewers have 10 days to trade him or release him. He is arbitration eligible, and the team was not expected to offer him a contract by Wednesday's deadline. Mench made $3.4 million last year.
With Mench and Geoff Jenkins gone, the Brewers now need to find a new left fielder.
The team will have to make another roster move if reliever Eric Gagne passes his physical and his one-year contract with the Brewers becomes official. The deal, reportedly worth $10 million, was agreed to this weekend.
Gagne would be the fourth reliever acquired by the Brewers since they lost Francisco Cordero and Scott Linebrink to free agency. They have traded for Guillermo Mota, signed free agent David Riske, and acquired Torres from Pittsburgh for two Minor League pitchers.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.