The Marlins placed Cronin on the 15-day injured list Friday with left knee tendinitis, Christina De Nicola of MLB.com reports.
Cronin dealt with an undisclosed injury a few weeks ago, but it's unclear whether that was related to his current issue. The reliever's season will end with him having posted a 4.35 ERA and 72:25 K:BB over 70.1 innings covering 56 appearances.