An MRI on Wednesday revealed the injury. The flexor pronator mass is the collection of muscles on the anterior of the forearm used for wrist and finger flexion as well as pronation. Buchholz allowed six runs and eight hits in 2⅓ innings against the New York Mets on Tuesday before the injury forced him to leave the game.
Buchholz has struggled in his first two starts since joining the Phillies from Boston, posting a 12.27 ERA.
Buchholz was a two-time All-Star with the Red Sox but has been trending downward since his best season in 2013 when he went 12-1 with a 1.74 ERA and helped Boston win the World Series.