St. John’s roster has been trimmed by one.

Freshman point guard John McGriff will redshirt this season due to a shoulder injury, he announced on Twitter Thursday night.

The 5-foot-9 Maryland native had been practicing up until a few days ago, a source said, but an MRI exam revealed he has been playing with a serious shoulder injury. McGriff tweeted that the doctor told him the injury could have a significant impact on his future if he didn’t address it.

Known as a hard-nosed defender, he was expected to be part of the rotation off the bench in first-year coach Mike Anderson’s pressing system.

The loss of McGriff leaves Anderson with three pure guards at the moment: Monmouth graduate transfer Nick Rutherford, sophomore Greg Williams and senior Mustapha Heron.

St. John’s is waiting to hear back from the NCAA regarding a waiver for Cleveland State transfer Rasheem Dunn. The combo guard from Brooklyn sat out last year while at Cleveland State and transferred after his coach, Dennis Felton, was fired. Anderson could also play big and use wings LJ Figueroa, Justin Champagnie or David Caraher in the backcourt.

St. John’s, which was picked by the Big East coaches to finish ninth in the conference, opens the season on Nov. 6 against Mercer at Carnesecca Arena in Queens.