Some of Tatum’s loved ones wouldn’t normally be inside the Celtics locker room after a game, but an exception was made to comfort him after he suffered what the team called a lower-body injury late in a 121-113 Game 4 loss to the New York Knicks. His mother, stepfather Marcus “Jake” Barnes and trainer Drew Hanlen were all there to provide support. As they emerged from a Madison Square Garden training room, where Tatum was apparently being evaluated, they looked tired, drained and concerned. Though several Celtics players and coach Joe Mazzulla said they didn’t know the severity of Tatum’s injury yet, before he was expected to undergo an MRI on Tuesday, the mood around the team painted a picture of pessimism. Enough fear surrounded his injury that even his teammates were reluctant to check on him. “He’s got people around,” said Kristaps Porziņģis, explaining why he had not seen Tatum yet. “It’s probably an overwhelming moment right now.”