Kolek (elbow) has been on a throwing program in extended spring training and is expected to return to game action by the end of the month, Tim Healey of the Sun-Sentinel reports.
Marlins president Michael Hill suggested Tuesday that Kolek has used his rehab from Tommy John surgery to smooth out his delivery, something crucial to the right-hander's development after he walked 61 batters over 108.2 innings in 2015 for Low-A Greensboro before being sidelined. The Marlins' No. 8 prospect is a long way from the majors, but he could emerge as one of the organization's top future assets if he looks good in the second half this season.