Mets pitcher Steven Matz in the first inning at Nationals...

Mets pitcher Steven Matz in the first inning at Nationals Park on July 31, 2018 in Washington, D.C. Credit: Getty Images/Patrick Smith

WASHINGTON — Steven Matz’s lengthy injury history might be getting longer.

The Mets are having the Long Island lefthander checked out by doctors Wednesday or Thursday, including a likely MRI, after he experienced tightness in his left forearm during his start Tuesday night.

The outing was the shortest of his career — two outs, with seven runs allowed — and Matz afterward said he has been dealing with a “dead-arm phase” for about three starts. Manager Mickey Callaway said the Mets knew about that, but the forearm discomfort was new.

“One thing to always remember with some of these guys is they haven’t a ton of innings in any one year it seems like,” Callaway said. “They’re all getting up there right now. So we all have to make sure that we understand that and take every precaution necessary to keep them on the field as much as possible.

“Maybe he’s hitting a little bit of a wall right now. We’re going to continue to check on him. I know he’s feeling a little better today.”

Matz, who has allowed 16 runs in 11 2/3 innings (12.35 ERA) in three starts since the All-Star break, is up to 107 2/3 innings this year, more than his 83 (majors and minors) last season. Matz has never passed the 140-inning mark because of health problems.

That injury history includes three surgeries on his left elbow: one in August 2017 to address an issue with his ulnar nerve, one at the end of the 2016 season to remove a bone spur, and Tommy John surgery in May 2010. Matz had a complicated Tommy John rehab, delaying the 2009 draft pick’s pro debut to 2012.

Staying on the mound has been a big part of Matz’s breakout year, though it doesn’t look as good after his ERA jumped from 3.79 to 4.35 Tuesday night. He said afterward he feels healthy, aside from the dead-arm issue, which Callaway said many pitchers deal with.

“I’m just trying to work through it,” Matz said. “It’s hard to describe. My stuff isn’t sharp like I want it to be.”

Evans hurt

Phillip Evans said he will have an MRI on his left knee Thursday. He exited the Mets’ loss to the Nationals Wednesday after one inning with what the team called knee discomfort, after he endured a takeout slide from Adam Eaton on a force play at second.

Callaway was unhappy with the ruling that it was a legal slide.

“I thought that rule was in place to keep that from happening,” Callaway said. “I thought it was a little bit of a slide that he kind of came off the bag, that’s why we challenged it, and our player ends up getting hurt.”

Extra bases

What do Noah Syndergaard and J.A. Happ have in common besides hand, foot and mouth disease? They both spent time at Yankee Stadium recently. “I’m surprised more people didn’t come down with it,” Syndergaard said. “I touched a lot of baseballs that day (July 20).” … Callaway said he dropped Brandon Nimmo, who had a .205/.359/.301 slash line in July, to sixth in the lineup to take some pressure off of him. “Nim is in the middle of trying to make an adjustment, back to the league that’s made a significant adjustment on him,” Callaway said. Nimmo went 0-for-4 and grounded into a game-ending double play … The Mets optioned Tim Peterson to Triple-A Las Vegas to make room for Syndergaard.