AP

The Dolphins won’t get to see what they have from rookie running back Jay Ajayi until the second half of the season.

Ajayi has been placed on injured reserve/designated for return. That means he’s out for eight weeks.

The move opens up a roster spot for the Dolphins, which they’ve used to sign quarterback Logan Thomas.

Ajayi slipped to the fifth round of the draft amid talk that he could have a knee injury, but any concerns about his knee seem to have been unfounded, as his knee has been just fine in Miami. In Thursday’s preseason game, he carried nine times for 66 yards and added two catches for 37 yards. Unfortunately, Ajayi broke a rib in the game, which is why he’ll have to miss the next couple months.

Ajayi was expected to provide some depth at running back behind Lamar Miller. Now the Dolphins are down to two backup running backs, Damien Williams and LaMichael James.