MINNEAPOLIS -- Nate Robertson wasn't available as the Tigers and Twins played through 13 innings Wednesday night. That's why Brandon Lyon took the loss in his third inning of work.

As it turns out, Robertson won't be available for a while. On Thursday, the Tigers made it official, placing Robertson on the 15-day disabled list with a muscle strain in his lower back and recalling left-hander Luke French from Triple-A Toledo.

The origins of Robertson's back issues date back to last weekend's series at Cleveland, possibly when Robertson was doing squats. Robertson said the injury seemed to be minor until the off-day Monday.

"It was tight going into the weekend in Cleveland, and it just finally came to a head," Robertson said. "I woke up Monday morning, and I couldn't get out of bed without using the nightstand next to me to push me up."

The Tigers had hoped -- really, had almost expected -- to be able to loosen it up in a day or two. That's why they didn't make the DL move Tuesday night, instead designating Juan Rincon for assignment to make room for Dontrelle Willis, whom the Tigers activated Wednesday to start the game that night.

"We weren't sure about Nate," manager Jim Leyland said. "We didn't find out until [Wednesday] afternoon that it would have to be a DL, and by then it was too late [to get somebody to Minneapolis from Toledo].

"There was nothing anybody could do about it. We did it right. We just got into one of those games."

French didn't get the call about the move until late Wednesday afternoon after the Mud Hens' game that morning and scrambled to get onto a flight to Minneapolis late Wednesday night. Even with the extra innings, he wouldn't have been able to get to the ballpark and into his gear to pitch had the Tigers made the DL move before the game.

"I felt really bad for Lyon going out there and having to throw 60 pitches," Robertson said. "And he's not the kind of guy that [normally] goes out and throws 60 pitches."

Not only was Robertson not available Wednesday, but Ryan Perry was off, too, after his two innings in Tuesday's game plus a side session. Had Lyon retired Joe Crede for the third out of the 13th inning, Leyland said his next pitcher would've been utility infielder Ramon Santiago, who last pitched as a kid in the Dominican Republic more than 10 years ago.

The 23-year-old French has enjoyed a solid opening season in the Mud Hens' rotation, posting a 2-2 record and a 2.91 ERA in six starts with 29 strikeouts over 34 innings. He earned the call over a lefty reliever, such as Clay Rapada, in part because of the role.

"We needed a long lefty desperately," Leyland said. "He was starting, so he fit into that role."

The Tigers backdated Robertson's move to May 6, his last appearance against the Twins at Comerica Park, so he's eligible to come off in a week. Robertson was hoping to at least be able to ride an exercise bike Friday.

Robertson believes he should be able to pitch by the time he's eligible to come off.