JUPITER, Fla. -- New York Mets left-hander Jonathon Niese abruptly departed Sunday's Grapefruit League game against the St. Louis Cardinals after two innings with elbow discomfort, casting doubt on his Opening Day availability.
Niese will fly to New York on Sunday night and undergo an MRI with team doctor David Altchek at the Hospital for Special Surgery in Manhattan on Monday.
Niese is likely to open the season on the disabled list regardless of the severity of the injury. If it is minimal, the Mets can backdate the DL stint nine days into spring training and have Niese make his season debut April 6 against the Cincinnati Reds, the first time the Mets need a fifth starter.
Niese believes the elbow injury is not significant. The southpaw indicated he initially injured it 10 days ago in an intrasquad game.
He said the discomfort is in the back of the elbow, not in the vicinity of the forearm ligaments that can lead to Tommy John surgery. He had been taking anti-inflammatory medication for 10 days, and added that the elbow did not pose a problem during his 2014 Grapefruit League debut on Tuesday.
It began posing a problem in the second inning Sunday when he hyperextended it on a pitch.
"It's the back of the elbow, which is good," Niese said. "I'm almost 100 percent sure it's nothing serious like Tommy John or anything. It's just a little discomfort. I wanted to go back out there. It's something that I could definitely pitch through.
"Actually, I felt great in the first inning. It was one pitch in the second inning -- I'm not sure which one -- it just felt like a stinger. It went away and I was able to pitch through it."
Niese had been dispatched to New York earlier in camp for an MRI of his left shoulder, but team doctors merely diagnosed him with weakness in the muscles of the scapula area near the left shoulder blade.
Five days ago, Niese alarmed manager Terry Collins with a first-pitch fastball that registered 79 mph. On Sunday, the Mets clocked Niese's fastball at a relative normal 89-90 mph during his 35-pitch effort.
Shoulder issues can cause a pitcher to unintentionally alter mechanics and affect the elbow.
"My mechanics were definitely off when I had that shoulder discomfort," Niese said. "After that, I think everything was fine."
Niese had been penciled in to be the Opening Day starter.
Niese missed two months last season with a rotator-cuff tear, but did not require surgery.
Assuming Niese opens the season on the disabled list, Jenrry Mejia could join Daisuke Matsuzaka in the rotation, with John Lannan earning a relief role. That trio had been the primary fifth-starter competitors, with Matsuzaka seemingly having the inside track.
Prospects Rafael Montero and Noah Syndergaard also remain in camp.
"It's the spring training from hell," Niese said. "I've never experienced anything like this. It's just frustrating."
Said assistant general manager John Ricco: "Any time one of our pitchers has something, especially in the elbow or the shoulder, we want to get it checked out. I would expect he will have an MRI shortly.
"I think he's frustrated because he's had a couple of different things that haven't turned out to be anything. But you want to have this smooth spring training. He hasn't had that this year.
"Hopefully it's like the last one, that he goes up and Altchek says, 'Don't worry about it,' and he comes back and moves on. Any frustration you hear, and from what he told me, isn't stemming from worry about the injury."
Collins said the Mets already had been considering keeping Niese in Florida for an extra start when the team broke camp and placing him at the back end of the first turn through the rotation.
"The positive is it's not his shoulder," general manager Sandy Alderson said. "But obviously as we get closer to Opening Day it becomes more and more problematic. Hopefully it's nothing serious, regardless of its impact on Opening Day."
ESPNNewYork.com contributor Todd Dewey contributed to this report.