BOSTON – Doug Fister already missed one month of the season with an injury in the left side of his torso. Now that the Detroit Tigers pitcher is back on the disabled list with a recurrence of the same injury, he is as curious as anyone what happens next.

“It's frustrating,” Fister said, “but it's just something I've got to do.”

Fister wants to hurry back, of course. But Tigers manager Jim Leyland insisted he wouldn't be rushed back, saying the pitcher “has to be 100 percent.”

“It's a fine line,” Fister said. “You've got to dance it, and you've got to take it one step at a time and figure it out from there.”

The right-hander was placed on the 15-day disabled list, retroactive to Tuesday. The Tigers called up Casey Crosby from Triple-A Toledo to fill Fister's roster spot.

Crosby will start Friday against the New York Yankees, in Detroit.

Fister was injured in his first start of the season on April 7. He made five starts since his return on May 7.

In the last of those, on Monday here, Fister said the discomfort gradually increased “once the adrenaline wore off and everything kind of settled down.”

“It was just kind of a progressive thing,” he said. “It wasn't a one-pitch deal.”

Leyland said pitching coach Jeff Jones had detected that Fister was altering his arm slot in recent starts, apparently seeking a comfortable release point. Fister disputed that contention but said the injury is “the same thing I felt before.”

“After the last start, I felt some soreness there in the side, and we took some action,” he said. “We got an MRI done (Wednesday) and we're going to compare it to the first one, and find out where we go from there.”

Email David Mayo at dmayo@mlive.com and follow him on Twitter at twitter.com/David_Mayo