The Pirates placed Peters on the 15-day injured list Monday, Jason Mackey of the Pittsburgh Post-Gazette reports. According to Alex Stumpf of DKPittsburghSports.com, Peters was deactivated due to a back muscle spasm.
The transaction is retroactive to June 3, he'll be eligible to rejoin the Pirates on June 18 if the back problem has subsided by then. Over 16 appearances (four starts) covering 25.2 innings this season, Peters has picked up four wins and three holds while logging a 3.86 ERA and 1.17 WHIP.