Rosenthal made one start this spring, on March 16 against the Twins, but had mixed results. In Grapefruit League play, he threw 10 innings over five outings with a 1.80 ERA, 11 strikeouts and a 1.50 WHIP.
Manager Mike Matheny dispelled any speculation of Rosenthal's status as a starter by announcing his five-man contingent in mid-March: Carlos Martinez, Adam Wainwright, Lance Lynn, Mike Leake and Michael Wacha, in order.
Once a lights-out closer who compiled 93 saves from 2014-15, Rosenthal struggled with pitch efficiency last year and missed seven weeks with right rotator cuff inflammation.