PORT ST. LUCIE — On a day Jacob deGrom was expected to put the final touches on a hopeful spring training leading into the season, he instead could be found in an MRI tube.

The Mets’ ace was set to get scanned at 9:30 a.m., the Mets said Friday, after feeling some tightness a day prior in his right (throwing) shoulder.

DeGrom was scratched from the start at Roger Dean Stadium against the Cardinals, which was set to be his final tune-up before the Mets open in Washington on Thursday.

It is still conceivable deGrom could get the ball on Opening Day — each starter was scheduled an extra day leading up to the start of the season — but the Mets have far bigger worries with a star who did not appear in a game after July 7 last season because of a low-grade tear of the ulnar collateral ligament.

DeGrom has been typically excellent — five innings, one run, 10 strikeouts — in a spring that had been smooth until he felt something in his shoulder while long-tossing Thursday.

The Mets will be starting Felix Pena in his place for the Grapefruit League game.