"The basic report was they think it's time," Leyland said. "He's throwing pretty much around the plate all the time, 89-to-93 [mph] -- some good breaking balls, some changeups. So he's used his pitches.
"He can't really benefit anymore down there. So it's time to find out. I think that's good. I think it's time to find out, too."
Willis will not be activated in Cleveland, but he will get side work in until his scheduled Wednesday start. Zach Miner will move to the bullpen to make way for the left-hander, who hasn't started a regular-season game since Sept. 27, 2008.
At Triple-A Toledo, Willis made two starts, striking out eight while walking six. When asked what expectations Leyland had for Willis upon his return, the Tigers skipper was adamant.
"I'll make that perfectly clear," Leyland said. "My expectations are for him to win games, like it is for every other pitcher that I put out there. There's no bones about that. This is not a gimmie situation. This is the big leagues, and we're trying to win.
"My expectations are that he will do well. I think he's got a very good chance to do that. We will see. But I'm 100 percent behind the move to get him here and to find out. This is not a trial. This is not experimental. This is not developmental. This is the big leagues."
Leyland suggested that another missing piece in the Detroit rotation, right-hander Jeremy Bonderman, could make a rehab start soon. Bonderman has been on the 15-day disabled list since March 30 as he recovers from thoracic outlet compression syndrome surgery.
"It looks like we're moving toward a point where [Bonderman] will be assigned somewhere, unless there are some surprising setbacks," said Leyland, adding that Bonderman threw six painless innings in extended spring training on Wednesday.
The potential return of both Willis and Bonderman finally would give Leyland a chance to use his full arsenal of arms.
Added Leyland: "I'm looking forward to having problems putting everything together."