DeGrom (6-5, 2.87 ERA) experienced shoulder soreness after his last start. He was examined by team doctor Struan Coleman on Monday at the Hospital for Special Surgery in Manhattan, and assistant general manager John Ricco said deGrom has been prescribed anti-inflammatory medication.
Manager Terry Collins expects deGrom to return after missing two starts.
"I'm very relieved," Collins said. "Actually, that's about as good as you could hope for, if that was all it's going to be. We'll give him a little downtime to get some energy and some strength back in his arm and be ready for the last month."
Montero, 23, went 0-2 with a 5.40 ERA in four major league starts in May and uncharacteristically walked 11 batters in 20 innings. The Mets believe Montero has regained his control in four Pacific Coast League starts since returning from a left oblique strain.
Montero was named the PCL Pitcher of the Week on Monday. He had tossed 14 2/3 scoreless innings over his last two Triple-A starts. He allowed four hits and four walks while striking out 17 in those outings.
"I've talked to [Triple-A manager] Wally [Backman] a couple of times, and one of the things that he said the other day to me is that he finally looked like he did last year -- where everything was in the strike zone," Collins said.
Montero was scheduled to pitch Monday for Las Vegas, so he'll be starting on an extra day of rest against the Nats on Tuesday.