(Photo credit: Bill Streicher-Imagn Images)

The Boston Celtics will have to face the Philadelphia 76ers in a do-or-die Game 7 without star Jayson Tatum, who will be sidelined for Saturday night's game with left knee stiffness.

Tatum did not play in the last 15 minutes of Thursday's Game 6 -- a 106-93 loss to the Sixers in Eastern Conference first-round play -- and was riding an exercise bike in the hall during the fourth quarter.

Tatum appeared to downplay the issue after the game, telling reporters, 'You guys probably saw when I went to the back, saw me on the bike. My leg just was a little stiff when I came out in the third quarter. But just kind of assessing the moment, the game was a little out of reach.'

The sore knee is not related to last May's devastating ruptured right Achilles tendon, Tatum said. That injury knocked him out in Game 4 of the Eastern Conference semifinals against the New York Knicks and kept him off the court until March 6 of this season.

'It was my other leg, not the one I injured last year,' Tatum said Thursday. 'I mean, I wasn't like overly concerned. ... I came out at four minutes, like I was supposed to. Just kind of assessed the game. (Celtics coach Joe Mazzulla) took the starters out fairly early in the fourth quarter.'

Mazzulla told reporters on a conference call Friday afternoon that Tatum would be available for Game 7, and Tatum said at Thursday's postgame press conference, 'I expect to play.'

Tatum has averaged 23.3 points, 10.7 rebounds, and 6.8 assists per game in the series against the Sixers.

In Game 3, Tatum became the fourth player in Celtics history to top 3,000 career postseason points. Tatum (3,076) trails three legends -- Kevin McHale (3,182), John Havlicek (3,776) and leader Larry Bird (3,897).

Tatum, 28, is a six-time All-Star, four-time All-NBA first-team selection and a two-time Olympic gold-medal winner for Team USA. Through 601 career NBA games, Tatum is averaging 23.5 points, 7.4 rebounds and 3.9 assists.

For the Sixers, Paul George was listed as probable with an illness for the game on his 36th birthday. Joel Embiid (post appendectomy) also is listed as probable, while Tyrese Maxey (finger) is available.

--Field Level Media