WALTHAM, Mass. — Jaylen Brown did not play in the Celtics' 117-101 Game 1 take-down of the Sixers and, though he declared he'd be back for Game 2, there is still uncertainty and caution.

Just before practice on Wednesday morning, Celtics coach Brad Stevens said Brown was doubtful to return to the lineup Thursday for Game 2.

Brown suffered a right hamstring injury in Game 7 of the Celtics' first-round series against the Milwaukee Bucks. That type of injury, though not severe to start, could easily become aggravated and potentially end Brown's season if care is not taken.

"The bottom line with this hamstring injury is that it's not terrible, it's not a long-term thing and it shouldn't linger if he comes back at the right time," Stevens said. "But you could make it worse if you don't come back at the right time if you have to guard JJ Redick or Marco Belinelli."

The assignment of tracking and chasing the Sixers' shooters is one unlike any other that the Celtics' young players have come up against, Stevens said.

Because Redick and Belinelli are constantly moving, running at full speed around tight screens and stopping on a dime for a quick release, aggravating the hamstring is a valid concern and the Celtics want to make sure they are being smart about when they bring Brown back.

Brown, who was slated to take part in a limited workout on Wednesday, will be reassessed by the Celtics' medical staff on Thursday before any final decision is made on his availability for Game 2.

From the outside, it might not have seemed that the Celtics were missing him in Game 1. But Brown, alongside Terry Rozier and rookie Jayson Tatum, has stepped up during Boston's injury-ravaged season and developed into a dangerous piece of the Celtics' young core and one of the team's most efficient two-way players.

"Jaylen, Jayson, and Terry, you start talking about all three of those guys, and growth has been huge," Stevens said.

Before Kyrie Irving was shut down in mid-March, Brown was averaging 14.1 points per game while shooting 46 percent from the field and 37.3 percent from three. He closed out the season by putting up 17.2 points per game, shooting 49.1 percent overall and 57.1 percent from beyond the arc.

In the six playoff games before his injury, Brown was averaging 20.5 points per game, twice scoring 30 or more.

"Imagine the expedited learning curve that Jayson Tatum is on, that Jaylen Brown is on: the empowerment, the minutes, the scoring need," Sixers coach Brett Brown said following his team's practice at Harvard University on Wednesday. "I bet in the light of day, they'll look five years back and think that opportunity really catapulted those two players, or Rozier, without Kyrie. They will reap the benefit of expedited growth."

Even with a Game 1 win under their belts, the Celtics know a playoff series can change quickly. They're anticipating each game against the Sixers to get more difficult and nuanced than the one before it. They also know how valuable Brown is to the team and would welcome his return – as soon as it is safe.

"[Brown, Tatum, and Rozier] just keep getting better, and you know what? They're going to have to play better as this series go on," Stevens said of his young stars. "There's some things obviously that we all can do to improve game-to-game and we'll have to do that."