Ethan Martin exited Thursday's game in Dunedin with right shoulder discomfort.
Martin was visited by the Phillies coaching and training staff twice during the fifth inning of the exhibition game against the Blue Jays. He walked off with a trainer at the conclusion of the second meeting.
Martin will be examined by the team's medical staff on Friday morning.
Martin faced just four batters in the inning; he did not retire a batter. The 24-year-old righthander allowed three runs on three hits and a walk.
The injury to Martin is another blow to an already short supply of starting pitchers in camp.
Jonathan Pettibone has been dealing with shoulder soreness this month. Miguel Alfredo Gonzalez has looked rusty. Cole Hamels entered camp two weeks behind the rest of the pitchers after dealing with biceps soreness in November.
Roberto Hernandez, the favorite for the fifth starter's job, suddenly has little competition.
David Buchanan, Jeff Manship and Sean O'Sullivan are also in camp as potential starting pitchers. The Phillies are also stretching B.J. Rosenberg out some this spring to have flexibility.