DETROIT — No doubt about it, Corey Knebel is one of the Detroit Tigers’ hottest minor-league commodities.

But when the Tigers decided Thursday they were bringing him up, there was one snag: He was not yet on the 40-man roster.

The Tigers took care of that Friday, when they actually made the transaction, outrighting the contract of Francisco Martinez to Double-A Erie. Robbie Ray was sent to Triple-A Toledo after Thursday’s start to clear room on the active roster.

According to MLB.com’s preseason list, Knebel ranked as Detroit’s 16th-best prospect (Ray was No. 3). Martinez used to be perceived that well.

When he was included in the trade to bring Doug Fister to the Tigers from the Seattle Mariners, Martinez was ranked as the No. 4 prospect in the Detroit farm system. After a disappointing stint in the Mariners’ system, Martinez was sent back to Detroit in trade, after being designated for assignment last June.

The Tigers had to designate Quintin Berry for assignment to add Martinez to the 40-man at that time, and ended up losing him, before seeing him again in the playoffs with the Red Sox.

After hitting .295 with 13 doubles and three home runs with Hi-A Lakeland in his return to the Tigers’ system last season, Martinez is hitting .228 with one home run and five doubles in 37 games with Erie this year.