The Cubs announced that Peterson will be moved to the bullpen after Edward Cabrera (hamstring) was reinstated from the 15-day injured list Sunday, Patrick Mooney of The Athletic reports.
Rather than expanding the rotation to six men to accommodate Cabrera's return, manager Craig Counsell will instead send Peterson to the bullpen to provide the club with another multi-inning arm to replace Javier Assad, who was optioned to Triple-A Iowa on Sunday. After a disastrous run in a swingman role with the Mets to begin the season, Peterson had pitched more credibly as a full-time starter for the Cubs since being acquired in late June. Over his eight starts with Chicago, Peterson went 4-1 with a 4.19 ERA, 1.37 WHIP and 31:16 K:BB across 43 innings.