ATLANTA — The Boston Celtics will likely be without their best perimeter defender for the rest of the opening round playoff series against the Atlanta Hawks.

Guard Avery Bradley sustained a severely sprained right hamstring in the fourth quarter of a Game 1 loss.

Before the Celtics practiced Sunday at Georgia Tech, coach Brad Stevens announced that Bradley was out for Game 2 and probably won’t return in the best-of-seven series. Bradley remained at the team hotel, undergoing treatment.

“Avery has a pretty significant strained hamstring,” Steven said. “He’ll continue to get treatment around the clock and go from there.”

Bradley was injured near the midway point of the fourth quarter, crumpling to the court right after the Celtics had come all the way back from a 19-point deficit.

“I tried to go up and block (Jeff) Teague, and when I came down, I felt weird,” Bradley said after the game. “I took a few steps and I just couldn’t walk.”

Without him, the Celtics struggled to contain Teague, who took control of the game in the closing minutes. The Atlanta point guard scored or assisted on 13 of his team’s final 22 points as the Hawks held on for a 102-101 victory.

The series resumes Tuesday night in Atlanta.

“It definitely hurts our team,” Celtics backup guard Marcus Smart said. “We lost another guy that brings it every night. Everybody else has to step up now.”

The Celtics will surely be relying on Smart and Evan Turner to take on bigger roles, even though neither is as accomplished at the defensive end as the 6-foot-2 Bradley. Also, rookies R.J. Hunter and Terry Rozier could get more playing time. James Young, a second-year swingman, is another option.

The question is: What sort of rotation does Boston go with now?

The Celtics have largely relied on a starting unit that includes Bradley and 5-9 Isaiah Thomas in the backcourt, and no one taller than 6-9 up front. They could opt for a more customary approach – 7-footer Kelly Olynyk has started eight games this season – or go even smaller, putting up to four guards on the court at one time.

“We’re playing small anyways, so you might have to go even deeper into that,” Stevens said. “We’ll have to decide if we’re going to go with some of those young guys and … play four smalls again, or if we’re going to play more traditional again and go back to playing that way. We’ll look at it and figure that out over the next 48 hours.”