Celtics coach Brad Stevens said tests on Brown's hamstring came back negative but the team is uncertain whether he'll be ready for the start of the series, given the quick turnaround.
Brown tweaked the hamstring during Saturday's Game 7 win over the Milwaukee Bucks and sat out the second half.
"The last email I saw [from trainers is] that [Brown] still has some soreness. Didn't try to do anything, that I know of, running-wise today," said Stevens. "He did have some testing, and that looked good, thankfully. Doubtful for tomorrow. But I guess he could play ... [and] it looks like it could be something that allows him to play as the series goes on."
Stevens wouldn't reveal who might start in Brown's place if he's unable to go.
"We could go either Marcus [Morris or Smart] starting, we could keep Semi [Ojeleye] in there, or Shane [Larkin]," said Stevens. "We've got to fill out one more spot, so we'll do that. We'll decide that [after Monday's morning shootaround]."
Celtics big man Al Horford said he talked with Brown when Boston gathered to watch film Sunday. But Horford wasn't sure whether Brown would be able to play in Game 1 and thinks Boston players are used to the next-man-up philosophy at this point in such an injury-heavy season.
The Celtics are currently playing without All-Stars Gordon Hayward and Kyrie Irvingas well as backup big man Daniel Theis.
"Obviously [Brown is] a big part of what we do, but I really don't know what his status is," said Horford. "So, again, we've been through it all year. Some of our guys need to get ready and rise up for the occasion. And I expect some of those guys off the bench to come in and provide us that spark."
Added Celtics centerAron Baynes: "We'll miss Jaylen. He's definitely hard to make up for, but it's just going to be about trying to collectively do it."
Brown leaves game with hamstring injury
Jaylen Brown heads to the locker room with a hamstring injury in the second quarter of Game 7.