PORTLAND, Ore. — The Celtics say All-Star point guard Kyrie Irving is set to have surgery Saturday to alleviate pain in his left knee.

Irving has been out since March 11, missing the last four games. There is no timetable for his return from the "minimally invasive" procedure.

Celtics coach Brad Stevens was asked before Boston's game in Portland on Friday night the ramifications of Irving's surgery.

"I don't know yet," Stevens said. "He's going to have it tomorrow and we'll know more about timelines after that."

The knee is the same one that Irving injured in the 2015 NBA finals that required surgery.

Irving is averaging 24.4 points, 5.1 assists and 3.8 rebounds per game. Friday was his 26th birthday.

He is one of several key sidelined players for Boston, which is at Portland on Friday. He joins Jaylen Brown (concussion protocol), Marcus Smart (thumb surgery), Daniel Theis (knee surgery, out for season) and Gordon Hayward (ankle surgery rehab).

Stevens said the team will focus on its strengths in light on the injuries.

"Do what you do best. That's it," he said. "Everybody's got something they do well otherwise they wouldn't be in the NBA. Don't try to be something you're not, don't try to make up for Kyrie's absence, or Smart's absence, or Tyson's absence by trying to do what they do. Just do you and just be good at it, be reliable at it. That's all we're going to ask."

Stevens said he had not had a lot of discussion with the front office about adding another player.

"I think that there is the possibility of applying for an exception again because of all the knee injuries and the length of injuries. I don't know where we are with that, and I haven't talked to them about any particulars.

He said if the Celtics added anyone it would be to give the team perimeter depth.

The Celtics are currently in second place in the Eastern Conference, below the first-place Toronto Raptors.

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