Fister, sidelined for the past week and a half with a left side strain, threw his first mound session Saturday afternoon and felt sore on Sunday. For now, though, the Tigers are treating it as a typical reaction to picking up the intensity on his throwing.
Fister will rest for another day or two, then throw another session and see how he feels, head athletic trainer Kevin Rand said Sunday. If he feels fine after that, he should be close to a return.
With Wednesday out of the question for Fister, the start that night against the Cubs will fall to Rick Porcello on his regular four days' rest. Justin Verlander will still start Thursday afternoon's series finale against the Cubs.
Casey Crosby, whose spot will be skipped coming out of Monday's off-day, will be available out of the bullpen for the next couple days before rejoining the rotation for Friday's series opener against the Rockies at Comerica Park.