PORT ST. LUCIE — Add Michael Conforto to the list of injury concerns for the Mets.

The outfielder tweaked his side making a catch and headed back to New York on Monday night to get checked by team physician David Altcheck after undergoing an MRI exam.

Conforto suffered the unspecified injury on Saturday, when he went 1-for-2 in a win over the Nationals. He didn’t play Sunday in Port St. Lucie or Monday in Jupiter, Fla., against the Marlins.

The 27-year-old has been one of the most durable players on the Mets in recent years, missing just 20 games over the past two seasons.

He’d gotten off to a sluggish start to the spring, going 6-for-27 with two extra-base hits, a walk and six strikeouts, but is coming off three straight excellent seasons at the plate.

Regardless of what kind of Grapefruit League season Conforto had, he’d be penciled in as the starting right fielder, with Brandon Nimmo perhaps splitting time with Jake Marisnick in center and J.D. Davis getting time in left field while the team tries to find out if Yoenis Cespedes can still be productive.

Already with several question marks in the outfield, a lengthy absence by Conforto would be especially damaging, especially with him expected to be in the middle of the lineup.