BOSTON -- Boston Celtics guard Jaylen Brown, who escaped serious injury when he hit the back of his head and neck late in the third floor of Thursday's game in Minnesota, has entered the NBA's concussion protocol.

Brown will be out indefinitely, the Celtics said Friday.

Brown crashed hard to the floor after slipping off the rim on a two-handed dunk. He walked off the court on his own and later left the arena to undergo a CT scan. He rejoined the Celtics for their trip to the airport and traveled with the team back to Boston.

Jaylen Brown left the court in Minnesota under his own power, but he's now in the concussion protocol. Hannah Foslien/Getty Images

"I probably had one of the better looks [at the fall]," Celtics big man Al Horford said after Boston's victory Thursday. "I was right there. It was just tough to see. I was just happy that he was able to get up and walk on his own power. That's probably one of the worst falls I've seen."

There was a strong sense of relief within the Celtics locker room after the game. Players on both teams stood quietly on the floor while Brown was initially checked out.

"It was a nasty, scary fall," teammate Gordon Hayward said Friday from the team's facility. "I haven't had a chance to speak with him yet -- he didn't come into the facility this morning -- but very blessed that nothing happened so far. It seems like he thinks he's OK; he was able to walk off. You have scary moments like that when you're in the air."

The Timberwolves' arena went hushed in the aftermath -- very much like Cleveland's Quicken Loans Arena when Gordon broke his ankle on opening night.

"You're hoping that he's OK. It happened so suddenly, too, like he didn't expect it," Hayward said of Brown's fall. "Then it just happens and you're hoping that he's OK. When he's able to finally walk off, you're at least a little bit relieved."

The Celtics' next game is Sunday at home against Indiana.