WASHINGTON -- Adam Eaton is scheduled to undergo an MRI on Tuesday after manager Dave Martinez admitted the team has some concern about Eaton’s right knee, which tightened up on him and forced him to exit in the third inning of the Nationals' 7-3 loss to the Mets on Monday.

Eaton was making his first start since Wednesday, when he was hit on the knee by an errant pitch. He did not start any of the next three games -- although he did pitch-hit on Friday -- before feeling good enough to return to the lineup on Monday.

"I'm a little concerned,” Martinez said. “He got loose, all good, didn't bother him at all. All of a sudden, it just kept getting tighter and tighter as a couple of innings went by.”

Eaton attempted to remain in Wednesday’s game after being hit, but he was removed after limping into third base running from first on a double. He did not believe the injury would be anything serious.

“Once he was moving around, he was OK,” Martinez said. "But just standing still, what got me nervous was he said it was more the back of his knee, which is a hamstring deal. I didn't want to take any chances. We are going to see where we're at.”

After injuries stemming from a torn ACL interrupted much of the Eaton's first two seasons in Washington, he has been much healthier this year. He has raved about how good his body has felt lately and had been heating up at the plate.

Eaton has played in 128 games, batting .288/.376/.435 and serving as one of the lineup's table-setters, along with Trea Turner. If the Nats need to replace him, they would have limited options. Gerardo Parra, who replaced Eaton in right on Monday, has been the primary backup outfielder, but he is 2-for-his-last-33 at the plate. He did contribute a high point in Monday's loss, with a diving catch to rob Pete Alonso of a hit.

“We got to pick [Eaton] up,” Turner said. "We’re going to need to play good without him, because he's been such a big part of our ballclub -- I don’t know how long he'll be out, and hopefully maybe not too long. I don’t know what the word is, but we need to step up and fill in that role, because he's had huge games for us all year and he's very important to us."