Walker is dealing with a bone bruise in his left knee that he suffered in Game 2. Williams left Game 3 with a sprained left ankle and has been dealing with turf toe for several weeks.
Celtics coach Brad Stevens said before the game that he didn't expect Walker or Williams to play as Boston looks to even the series at two games apiece.
Stevens said Walker felt something in his knee in Game 2, and he was listed on the injury report with a bone bruise before Game 3. While he did get eight rebounds in Boston's 125-119 victory, he also shot 3-for-14 from the field and scored just six points in 34 minutes.
"I don't know what the exact moment was, but he said he felt it in Game 2," Stevens said. "He had three days off in between Game 2 and Game 3 but was really sore. He has his typical knee work that he does in between each day and each game, and then the bone bruise on top of that, and then was more sore after Friday's game than he was even before that.
"He felt good enough to play [in Game 3, then] didn't feel very good yesterday. Was hoping that that would dissipate today, and didn't feel much better this morning."
Walker missed the first few weeks of the regular season after going through a 12-week strengthening program to build up his left knee after it bothered him for most of 2020. He also sat out half of every back-to-back set the Celtics played in 2020-21 as part of an ongoing maintenance program that the team hoped would allow him to get through the season healthy.
In total, Walker missed 29 games this season. By comparison, he missed a combined 35 games through the first eight years of his career with the Charlotte Hornets -- 20 of which came in one season.
"Probably a combination of them," Stevens said, when asked if Walker was dealing with only the bone bruise or if the knee soreness was also to blame. "But he's sore. ... He's dying to play. It hurts if he's unable to. He's not a guy that likes to miss, especially with the anticipation of getting back in this series."
Williams has been dealing with a case of turf toe on his left foot for several weeks, an injury that caused him to miss several games late in the regular season. But he came back to have a terrific performance in Game 1, in which he was a disruptive force at both ends against Brooklyn's weak interior play -- including recording nine blocks.
But he played only six minutes in Game 3 before exiting with the sprained ankle, and Stevens said Williams -- whom he called the team's "wild card" heading into Game 3 -- was dealing with plenty of pain.
"The ankle injury is not like a high ankle sprain or anything that's too significant, but he is really sore," Stevens said of Williams. "[With] the turf toe on top of that ... he tried to give it a go the other night and didn't look like he was moving at all. He spent the better part of each of these off days in a boot. He has not felt any better."
For Brooklyn, forward Jeff Green remains in a walking boot with his plantar fascia strain and has already been ruled out for the rest of the series.