X-rays taken at Citi Field were negative according to Nationals manager Matt Williams, and Ramos will be further evaluated by a hand specialist on Tuesday.
Ramos, who went 0-for-3, struck out to lead off the top of the seventh inning. He was replaced behind the plate by Jose Lobaton to start the bottom of the seventh.
"There was a foul tip, and he took a swing that he didn't feel good on," Williams said. "So we got him out of the game at that point."
The 26-year-old from Venezuela missed 59 games last season due to a hamstring injury. But when healthy, he was very productive at the plate, batting .272 with 16 home runs and 59 RBIs in just 78 games. The 16 homers was a team record for catchers.
Williams had Ramos in the cleanup spot Monday, one place ahead of Bryce Harper.
"He works really hard," Williams said of Ramos, who was not available to reporters. "Anybody on our team, you don't want to see that on Opening Day -- any time, but especially on Opening Day. We'll see where we're at [Tuesday]."
Speaking of Harper, his 2014 season almost got off to a disastrous start.
After walking in his first at-bat in the top of the second inning, Harper was running to second base on a ground ball to third by Ian Desmond. On a hard slide, he collided with Mets second baseman Eric Young Jr., who was trying to turn a double play.
Harper's head met Young's knee, and Harper remained down for a couple minutes, before eventually sitting up and then walking off the field escorted by a trainer. Harper was out at second on the play, but did remain in the game, going 1-for-4 with a single, a walk and two strikeouts.
"[Young] just got me with his knee or his shin and blew me up a little bit," Harper said. "I feel OK now, just got a pretty bad headache and things like that. No haziness or dizziness or anything like that, so that's a plus. But my head hurts pretty bad right now."
Harper said he passed two concussion tests -- one right away before returning to the game, and another one after the game was over.
"I didn't see stars or anything," Harper said. "I've seen stars before. So I knew I was gonna be OK."
The 2012 National League Rookie of the Year has a habit of putting his body in harm's way.
"That's the way Bryce plays, he plays hard," Williams said. "Those things are gonna happen from time to time. But the doctor cleared him up and he should be good."
The Nationals came from behind to beat the Mets 9-7 in 10 innings Monday. The teams are off Tuesday before resuming their season-opening three-game series Wednesday night.