Irvin (shoulder/lat) will undergo an MRI on Sunday, Mark Zuckerman of NatsJournal.com reports.
Irvin spun five scoreless and hitless innings Saturday, earning the win against Atlanta despite feeling something in the back of his shoulder/lat area during the contest. He tried to throw a warmup pitch prior to the sixth and still felt it, and so the Nationals made the call to remove him from the game. The right-hander will undergo imaging to determine the exact nature and full extent of the issue -- one which Irvin told manager Blake Butera he's dealt with in the past.