Williams, who was hurt in the fourth quarter of a win Friday night, took part in a walkthrough at Philips Arena on Saturday before the team departed for Boston. But his knee was iced and heavily taped, and he didn't even attempt to bend it during the light, 30-minute workout.
Coach Mike Woodson remains hopeful that Williams will be on the court. Besides his offensive contributions, he's a key part of the Hawks' defensive package, usually assigned to Boston star Paul Pierce.
"My gut says Marvin is going to play," Woodson said. "This is Game 7. He's put all his hard work from this summer into the regular season, and now he's got Game 7 with the best team in the league."
Williams was hurt with just under 9 minutes left in Friday's game when he bumped into Pierce as the Celtics' forward was driving toward the hoop. Pierce stumbled into Williams knee, which twisted awkwardly, and the Atlanta player immediately headed to the bench.
"It did not feel very good at all," Williams said.
The Hawks initially said he would not be able to return, but he re-entered to play defense with 20 seconds left and the Hawks clinging to a 100-98 lead.
"It could have been our last game," he said. "I definitely wanted to be there for my team. At the end of the game, they put me in there for some defense and I was able to help us get a stop."
Pierce also was hurt in the collision.
Celtics coach Doc Rivers said Pierce skipped Saturday's walkthrough because of a bruised right hip.
"Not because he couldn't, but because there was no point in him being out there if he's hurt," Rivers said.
Pierce was not available for comment after Friday's game or at Saturday's practice.
Williams, the No. 2 overall pick out of North Carolina in 2005, averaged a career-best 14.8 points a game this season. In the playoffs, he's fourth on the team with a 12.2 average, but he came up with a big effort in Game 6 of a series that has lasted much longer than expected.
Williams hit 6 of 9 shots from the field, made all six of his free throws and helped hold Pierce to only six points after the first quarter.
"I'm sure I'll give it a try in warmups," Williams said. "I definitely don't want to put myself at any greater risk of injury. I'll try to play it safe, but at the same time I want to be there for my teammates."