Stevens said Thomas, who returned home to Tacoma, Washington, to be with family following the death of his younger sister, is expected to rejoin the team late Thursday night and be ready to play in Friday's Game 3 of a first-round series against the Chicago Bulls.
The Celtics are hopeful that Thomas' brief trip home will help him cope with loss of Chyna Thomas, who died Saturday in a one-vehicle accident in their home state of Washington. The rest of the Celtics' roster traveled to Chicago on Thursday afternoon.
Teammate Avery Bradley said he talked with Thomas on Thursday and thinks the visit will help Thomas as he grieves.
"Being with family at a time like this I think is very important and it's very helpful," said Bradley, a fellow Tacoma native who has helped console Thomas in recent days. "And us being his extended family, I think us continuing to send him positive texts, I know that always helps."
The top-seeded Celtics, down 2-0 after dropping the first two games of the series in Boston, have acknowledged the cloud hovering over the team since Thomas lost his sister and players are trying to work through the emotions with a goal of playing more inspired basketball than they've displayed thus far.
"There's been a lot going on since before the playoffs started with the whole Isaiah situation," said Marcus Smart. "That's a lot of burden on his shoulders, and it affects us, too. That's our brother and when he goes through it we all go through it.
"You can see it in Isaiah. He's never missed six free throws in a game in his career [like he did in Game 2]. We just have to get together. It's good for him to have this break and go to see his family. We just have to come together as a group."
Stevens was noncommittal when asked about whether the Celtics would make any changes heading into Game 3 after being outplayed in Tuesday's Game 2 loss.
When pressed on possible changes to the starting lineup, Stevens said simply, "I don't know. Maybe. We'll see."
The Celtics have been dominated on the glass in each of the first two games of the series, giving up a total of 26 offensive rebounds in the first halves of those games.
When Boston struggled early in a first-round series against Atlanta last season, Stevens inserted Jonas Jerebko and Evan Turner into the starting lineup and Boston won twice to even the series before bowing in six games.
Stevens has often resisted the urge to tinker this season, particularly given the way his starting lineup thrived when everyone was healthy this season. During Tuesday's Game 2, Stevens went with Tyler Zeller as the second-half starter at center in place of Amir Johnson and Boston was more competitive on the glass.
Celtics forward Jae Crowder acknowledged that something has to change for the Celtics.
"I think we gotta adjust, in some way, some fashion. Something has to change," said Crowder. "Whether it be a coverage, whether it be a lineup, whether it be anything, something has to change because [the Bulls] are comfortable at this point. The playoffs are all about adjustments."
Crowder said the first two games of this series hasn't been a reflection on how Boston can play.
"Obviously, that's not us," said Crowder. "We know that. But you have to look at [the film]. As bad as it hurts to watch, you have to look at it and learn. Film doesn't lie. I've been looking at it and we're about to look at it as a group together, Game 2, and we have to get better from it."