(Reuters) - A sore right shoulder forced Philadelphia pitcher Roy Halladay to exit their 8-3 loss to St. Louis in the second inning on Sunday, adding to the injury concerns of the struggling Phillies.

Halladay (4-5), twice a Cy Young winner, has endured a rare, rocky start this season and said he had felt pain in his throwing shoulder during his previous start.

"You have this stuff from time to time, and most times, if you take care of it, it kind of goes away," Halladay told reporters. "But it never seemed to go away."

Halladay will be examined on Tuesday when the extent of the injury will be determined.

The Phillies have already been playing this season without injured standout hitters Ryan Howard and Chase Utley.

Having won the National League East Division for five consecutive years, Philadelphia find themselves in the unfamiliar position of last place so far this term.

(Writing by Jahmal Corner in Los Angeles. Editing by Patrick Johnston)