Branch had his knee re-examined in New York on Monday, but will also have an MRI on Tuesday.
His status for Wednesday's game against Connecticut is uncertain.
Branch went down in a tangle under the basket and could not put any weight on the leg afterward. Branch was treated with ice, and was returning to New York with the team.
"Because we're so young, we need to be as close to full strength as we can be," St. John's coach Steve Lavin said. "We hope he's gonna be OK. We don't have enough information at this point from the trainers and the doctors, other than the sprained knee."
Branch, a sophomore who just became eligible in late December after transferring from Texas A&M midseason last year, had started the past six games for the Red Storm. He was third on the team in scoring, averaging 9.0 points per game.
"Jamal, he's our general on the floor; he's an extension of our coach on the floor," said forward Jakarr Sampson. "It hurt a lot when you see him going down clutching his knee, having to get carried off the court."
Branch spent the rest of the game on the bench, watching the game with a towel draped around his face. He was not made available to the media after the game because of the injury.
"He's kind of hurt right now," Sampson said. "Kind of sad. But he's gonna be all right."