Wheeler, who underwent Tommy John surgery on March 24, 2015, had been scheduled to pitch an inning against Gulf Coast League competition early this week to begin ramping up for a return to the majors. Instead, he will be examined by team doctors on Wednesday at the Hospital for Special Surgery in Manhattan.
General manager Sandy Alderson said the gravity of the elbow issue is unclear until Wheeler is examined by team doctors.
"All I can say is he's had a little bit of elbow discomfort," Alderson said. "He hasn't thrown in a couple of days."
He had one hiccup this April, when doctors needed to go back into the elbow to remove an undissolved stitch from his original procedure.