DETROIT -- Six weeks after Luis Marte pulled his left hamstring in the final game of Spring Training, the right-hander is back pitching in actual games. He's just doing it in the Minor Leagues for now.

After two outings in extended spring camp, the Tigers sent Marte out on a rehab assignment to high Class A Lakeland. He was scheduled to pitch for the Flying Tigers on Thursday night against Port St. Lucie, the Mets' Florida State League affiliate.

The Tigers can keep Marte on rehab for up to 30 days, whether in A ball or at a higher level. There's no strong indication whether the Tigers would do that or not, given the state of their bullpen compared with the amount of time Marte lost. If they go the full 30 days, though, they'd have to decide from there whether to activate Marte or option him to the Minors.

A day before the injury, the Tigers had announced that Marte was slated to make the Opening Day roster. His injury created a spot for left-hander Duane Below, who has been on the big league club all season.

Detroit has had a relative revolving door elsewhere in the bullpen, from Daniel Schlereth to Thad Weber to two different stints for Brayan Villarreal, who was just recalled from Triple-A Toledo on Thursday.

Abdominal strain keeps Jackson out of lineup

DETROIT -- Austin Jackson's abdominal strain remains a day-to-day situation, the outfielder said Thursday morning. Thursday, however, was not a day for his return.

Jackson said after Thursday's loss to the Twins that the injury felt about the same as it did when he first suffered it Wednesday. He had it wrapped for treatment before the game and was moving around the clubhouse, but he sounded unlikely to be available at all against the Twins.

"It's pretty much still day-to-day," Jackson said after the game. "We're going to see how it feels tomorrow and kind of go from there. I really didn't expect it to feel any different today, just because it happened last night. Getting up early, it was a little stiff. That's pretty much what I expected. ...

"I think it's just going to take a few days to really get a good idea of how it feels, start moving around and twisting and bending, things like that."

Whether that rules out this weekend's series against the Pirates, Jackson said, he wasn't sure.

"It just depends on how it feels when I come in each and every day," Jackson said.

If the Tigers can get Jackson back for this weekend's series against the Pirates, they'd likely be overjoyed. In the meantime, though, his injury -- combined with Wednesday night's roster move to add Brayan Villarreal as an extra reliever -- left the Tigers with just two players available off the bench.

One of those bench players is backup catcher Gerald Laird. The other reserve available Thursday was utility infielder Ramon Santiago, who pinch-hit for Don Kelly, Jackson's fill-in at leadoff and center field.

"I don't know how long we'll play without Jackson," manager Jim Leyland said Thursday morning. "I don't foresee it being a long time, but you never know."

Leyland: Porcello could be overthrowing

DETROIT -- Tigers manager Jim Leyland reiterated Thursday that while Wednesday's four innings from Rick Porcello weren't good enough, he wasn't criticizing Porcello or suggesting any sort of change.

The only adjustments will be the tweaks that Porcello and pitching coach Jeff Jones make between starts, with an extra day before Porcello's next outing Tuesday in Cleveland.

On that front, Leyland agreed with Porcello's remarks from Wednesday night that he has to get his slider more consistent.

"My personal opinion," Leyland said, "is that while throwing harder has helped him, it's also probably hurt him."

Catcher Alex Avila knows the slider Porcello is trying to find, the one he had down the stretch last season. It was a hard slider, sometimes acting like a cutter, and it gave him a deceptive pitch to throw off of his sinker.

Porcello has had that pitch at times this season, but not always.

"This year, he's having trouble finding a release point," Avila said.

While Porcello is throwing harder this year -- the average velocity on his fastball and sinker are both up about two mph, according to Fangraphs.com -- Avila believes he doesn't have to overthrow to produce that velocity. Part of it is that he's physically bigger.

"He's growing," Avila said. "He can throw 94 without having to throw it hard."