Mud Hens manager Larry Parrish told the Toledo Blade there was some issue with Putkonen's stuff.
"I didn't think he had the pop on his fastball, the movement," Parrish told The Blade's John Wagner. "There were also some things we don't want to talk about, but that we might be able to help him with."
Putkonen made three rehab appearances over the past week between Toledo and Class A West Michigan. He went on the 15-day disabled list a few weeks ago with right elbow inflammation.
The Tigers aren't in desperate need of relief depth just yet, thanks to a string of solid starts. They'll have about 2 1/2 weeks of games following Thursday's off-day in Boston, which could eventually set up the need for a long reliever.