Starting All-Star guard Kemba Walker will not play for the Boston Celtics in Saturday’s showdown against the Houston Rockets due to left knee soreness, the team announced in its injury report late Friday.

It’s a big loss for the Celtics (41-17), since the 6-foot-0 guard has averaged 21.8 points, 5.0 rebounds, and 4.1 assists per game this season. He shoots 38.8% from 3-point range.

With Walker out, the Celtics will likely start defensive pest Marcus Smart in the backcourt alongside Jaylen Brown.

In Walker’s absence, more of the scoring burden for the Celtics will fall on 21-year-old sensation Jayson Tatum. Now in his third NBA season, Tatum has averaged 36.7 points per game on 62.9% shooting and 62.5% from 3-point range over his last three games — all Walker absences.

The Celtics official injury report says that Kemba Walker is OUT tomorrow vs the Houston Rockets. Brad Stevens said that was likely the case. Robert Williams is listed as probable. — Keith Smith (@KeithSmithNBA) February 28, 2020

In Boston’s loss to Houston on Feb. 11, defensive stalwarts P.J. Tucker and Robert Covington helped the Rockets hold Tatum to just 15 points on 5-of-15 (33.3%) shooting, and 0-of-7 on 3-pointers. But the task will likely be even more difficult on the road.

For the Rockets, reserve guard Eric Gordon is listed as questionable due to a bruised knee — though Gordon said Wednesday that he plans to play. He’s averaging 15.2 points in 29.2 minutes per game this season.

Houston (38-20) enters Saturday’s showdown of NBA title contenders with victories in five straight games and eight of 10 overall, while the Celtics have won 11 of their last 13. Tip-off from TD Garden is scheduled for 7:30 p.m. Central, with the game televised nationally on ABC.