Perkins first started feeling spasms while warming up before his appearance against the Orioles on Sunday, but he was able to get through a scoreless inning. It's unrelated to the neck issue that caused the All-Star to miss five games before his return on Sunday.
Perkins was able to throw and move around before Thursday's game, and Molitor said before the game that Perkins will be able to avoid the 15-day disabled list.
"With that back thing, it's like it feels better for a while, but then it stiffens back up," Molitor said. "I'm not a back expert, but I know they can be a little bit fickle in terms of how they respond. Sometimes they can come and go really fast, and sometimes they linger. Sometimes it changes even hour to hour. So there's not a lot you can do. But it's not a situation where I'm thinking about DLing him."
With Perkins out, Kevin Jepsen has served as the temporary closer, picking up three saves, including one against the Rays in Wednesday's 5-3 win.
"He's frustrated," Molitor said of Perkins. "He's watching these games and how close they've been. We've had games to save and he hasn't been available, and I'm sure that's tough for him."
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, follow him on Twitter @RhettBollinger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.