Speaking after Monday's game, Walker did not express alarm about his shoulder.
"It's already feeling better now, but I'm gonna go for an MRI tomorrow just to know what we're dealing with, but feel pretty good about it," Walker said, adding that he did some testing on the shoulder that went well.
Walker was dominant before exiting Monday's game, retiring all six batters he faced while striking out four.
The shoulder issue Walker dealt with came on the heels of him being forced to leave his final spring training start because of a right knee problem.
According to Walker, the knee issue was a result of his doing lots of work on his lower half while trying to get his mechanics right in advance of the regular season.
Trevor May also left Monday's game early, with the reliever dealing with arm fatigue, but he isn't hitting the IL.
He tweeted a "thumbs up" emoji on Tuesday, when he was expected to undergo an MRI.
"Very, very low grade triceps strain," he said when asked exactly what his injury was, "which makes a lot of sense with stiffening up in the second inning. Usually when something’s barking a little bit, other things try to take over to help. That’s when you start to feel it.”
May, who said he usually deals with arm soreness early in the season, was asked to record more than three outs for the first time as a Met on Monday, and he said that, combined with the cold and still only being four weeks removed from reporting to spring training, led to the awkward feeling in his arm.
"It's been a little bit since I've done it [pitch more than one inning], so went out there and just didn't really loosen up. And that was kind of the first test of it anyway, so now I know," May said after Monday's game. "But it was nothing - there was no pitch or sharp pain or something went. It's all stuff I've felt before."
With Walker out, the Mets will likely insert David Peterson into Walker's spot in the rotation. Peterson gave the Mets 4.0 scoreless innings in relief of Walker on Monday night.
