"He wanted to go, fought me relatively hard in the office today about wanting to be on the mound tomorrow, taking a ton of pride in making every one of his starts," Padres manager Andy Green said after Sunday's 5-3 loss to the Giants. "I just thought the prudent path was to slow it down for one start and give that start to Jarred Cosart."
The Padres recalled right-hander Zach Lee to take Cahill's place on the 25-man roster. He'll serve as a reliever, while Cosart moves from the bullpen back into the rotation.
During the offseason, Major League Baseball reduced its minimum DL time from 15 days to 10 days (not including concussions). Because the Padres made the move before Sunday's game, Cahill's DL stint is retroactive to his start Wednesday, meaning the Padres could potentially use him for his next scheduled start -- April 16 in Atlanta.
"That's kind of where the 10-day DL changes things contextually from what's occurred in the past," Green said. "Now you have a starter, who, just because he's a little banged up, you don't have to put him out there. You can make a roster move and bring him back for the next one. That's my hope, my anticipation. With low-back stuff, you're never really 100 percent sure until it resolves itself completely."
The Padres signed Cahill to a one-year deal during the offseason. He had spent most of the previous two seasons pitching in relief for the Cubs. Wednesday's 99-pitch outing was his longest since August 2014. Cosart has spent his entire Major League career as a starter and made the second relief appearance of his career Thursday. He's coming off offseason surgery to remove a bone spur in his right elbow, which slowed him during Spring Training. Ultimately, Cosart missed out on the rotation during the final week of camp, with Cahill and Luis Perdomo earning the final two spots.
Lee, meanwhile, has made one big league appearance -- a 2015 start against the Mets in which he allowed seven runs over 4 2/3 innings. The Padres claimed Lee off waivers in December, and he posted a 3.60 ERA in three Cactus League appearances.
AJ Cassavell covers the Padres for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.