DETROIT -- Austin Jackson, who has missed about four weeks with a pulled left hamstring, could finally be nearing a Minor League rehab assignment as the hamstring frees him to run at full speed.

Jackson ran the bases on Saturday before batting practice, with encouraging results, as he had done the previous two days.

"He ran the bases very well," head athletic trainer Kevin Rand said. "It's the third day in a row we've been able to do that. Each day he's done progressively better. He went through all his normal baseball activities, what he would do to prepare for a game. We're just going to re-evaluate him tomorrow."

Rand didn't want to put a timetable on a rehab stint until Sunday's assessment.

Though Avisail Garcia and Don Kelly have filled in relatively well for Jackson in center field, the Tigers have missed Jackson's presence in the leadoff spot, with the impact being felt down the lineup.