DeGrom felt discomfort Friday while throwing a bullpen session at Pittsburgh, according to Rojas. An MRI hours later showed there was forearm tightness but no structural damage. The right-hander hasn't yet been slotted back into the rotation and there is no projection on when deGrom might pitch again. He is considered day-to-day.
"Right now, we're treating the player for what he feels,'' Rojas said. "That's how we're approaching day to day until he feels good and can throw."
DeGrom is 7-2 with a major-league-leading 1.08 ERA in 15 starts this season despite being hampered by multiple ailments. He last pitched July 7 against Milwaukee.
Rojas added that deGrom said Saturday that he felt similar forearm tightness during a bullpen session right before the All-Star break as well. DeGrom did not attend Tuesday night's All-Star Game at Coors Field in Denver, electing instead to spend time with his family and rest for the second half.
The two-time National League Cy Young Award winner skipped an outing between April 28 and May 9 because of discomfort in his right lat muscle, then did not pitch again until May 25 while spending time on the injured list with what the Mets said was tightness in his right side. DeGrom left his June 11 outing against San Diego after six innings because of flexor tendinitis in his right arm.
Rojas said Saturday that those ailments, including the right forearm tightness, are all unrelated.
The Associated Press contributed to this report.