Boston played without guard Dennis Schroder and center Robert Williams III in its 109-97 win at Toronto on Sunday. Schroder was sidelined with a right ankle sprain while Williams sat out with a non-COVID-19 illness.
Meanwhile, Celtics All-Star Jaylen Brown was a game-time decision as the team continued to manage his return from a hamstring injury. Brown played 27 minutes and scored 16 points.
Celtics coach Ime Udoka said Tuesday he was optimistic that all three would be in the lineup for the team's game against the 76ers.
Against Toronto, five Boston players scored in double figures, led by Marcus Smart with 21 points, eight rebounds and six assists.
The win snapped the Celtics' two-game skid after they fell to Brooklyn at home last Wednesday and at San Antonio on Friday.
"To be able to bounce back against a good team like Toronto, in their house, it just shows the type of team we are," Smart said. "We're always going to continue to fight no matter what."
Josh Richardson added 18 points off the bench after missing three games with a non-COVID-19 illness. Boston's defense limited Toronto to 37.6 percent shooting (35-of-93), although the Celtics shot just 41.5 percent (34-of-82) themselves.
"Defense has been steady, and we've maintained that pretty well," Udoka said. "Offensively, we know that if we get better in transition, we can make a leap."
Both the Celtics and 76ers enter Wednesday's matchup with 11-10 records after up-and-down starts to the season.
Philadelphia began its season with eight wins in 10 games before dropping eight of its next 11 amid a COVID-19 outbreak.
The 76ers' 101-96 win over Orlando on Monday snapped the team's two-game skid. Seth Curry led the way with 24 points while Tobias Harris added 17 with nine rebounds and Joel Embiid contributed 16 points and 13 boards.
The 76ers led comfortably for most of the first half before the Magic gained a third-quarter lead. Philadelphia led 81-78 going into the fourth quarter and the game was tied at 93 with just under a minute to play.
Embiid and Tyrese Maxey combined to sink eight free throws over the final 48.1 seconds to seal the outcome.
"It was a win, not inspired," 76ers coach and former Celtics bench boss Doc Rivers said. "I just didn't think we played very well. ... I'll take any win. I'd rather win these than lose these."
It was Embiid's second game back after he missed the team's nine prior contests due to a positive COVID-19 test. Embiid said after making his return against Minnesota last Saturday that he thought he "wasn't going to make it" amid his bout with the virus.
Harris also tested positive for the coronavirus in early November and missed six games.
Re-establishing chemistry, Harris said, "is going to be a process."
"We've pretty much had different lineups all throughout the season. It's going to be a process of rhythm and feel, and then also just gaining our chemistry of how we're going to play."
It is the first of four meetings between Philadelphia and Boston. The 76ers swept the three-game series between the teams last season.
--Field Level Media