Donovan Mitchell underwent a medical procedure on his nose on Tuesday and will be re-evaluated in about one week.
The injury timeline given by the Cavaliers means he'll likely miss two games against the Miami Heat, as well as contests against the Minnesota Timberwolves and Charlotte Hornets.
Depending on his recovery, the five-time All-Star has a chance to return for the second part of a home-and-home with the Hornets, next Wednesday at Charlotte.
Mitchell suffered a nasal fracture in Saturday's 117-103 loss to the Houston Rockets when he was accidentally hit by team-mate Tristan Thompson, and subsequently sat out Monday's 108-103 win over the Indiana Pacers.
With the victory, the Cavs improved to 10-9 without Mitchell, who has missed time lately with a bone bruise in his left knee.
They are 33-16 in games he plays.
Mitchell, 27, is one of the NBA's top scorers, ranking sixth at 27.4 points per game, while also averaging career highs with 6.1 assists and 5.3 rebounds.
His play is a big reason why Cleveland is in the mix for one of the top seeds in the Eastern Conference.
The Cavs entered play Tuesday in third place in the East, one game behind the Milwaukee Bucks for first place in the Central Division.
They are also just two games ahead of the New York Knicks, and three up on the Orlando Magic.
This is the latest significant injury for Cleveland, which has also seen starters Evan Mobley (ankle) and Max Strus (knee) both miss time lately.
The procedure was administered following consultation with specialists in October, the Celtics revealed in a statement on Tuesday.
He was subsequently put on a 12-week strengthening program to prepare for the 2020-21 campaign, which is tentatively scheduled to begin on December 22.
Four-time NBA All-Star Walker is expected to return to on-court activities this month, though a further update on his status will not be provided until the first week of January.
The Celtics acquired former Charlotte Hornets star Walker in a sign-and-trade deal last offseason, inking him to a six-year, $141million contract.
Walker averaged 20.4 points per game, his lowest average since he put up 20.9 in the 2015-16 season with the Hornets. His last season in Charlotte saw him manage 25.6 points per game.
That dip is likely partially down to his drop in minutes. Walker played 31.1 minutes per game in 2019-20, his lowest average since his rookie season (27.2).
Jayson Tatum, Jaylen Brown, Gordon Hayward and Marcus Smart all played more minutes than Walker, who scored 19.6 points per game in the playoffs as the Celtics reached the Eastern Conference Finals in the NBA bubble in Orlando, eventually losing to the Miami Heat in six games.
However, with Hayward signing a max contract with the Hornets, Walker's time on the court could increase when he recovers.
The Celtics also announced that forward Tristan Thompson will have his availability for the first week of training camp limited because of a minor hamstring strain suffered in an offseason workout.
The 2019-20 NBA campaign has been postponed since March due to the COVID-19 crisis, which has wreaked havoc globally – pushing the Olympic Games and Euro 2020 back a year.
At the time of postponement, Giannis Antetokounmpo and the Eastern Conference-leading Milwaukee Bucks (53-12) owned the best record in the league, ahead of LeBron James' Los Angeles Lakers (49-14), the Toronto Raptors (46-18) and Kawhi Leonard's Los Angeles Clippers (44-20).
It remains to be seen when, and if, the season will resume but Thompson said on Thursday: "Guys want to play."
The Cavaliers are an Eastern Conference-worst 19-46 and will miss the playoffs for the second consecutive season.
Thompson, who is eligible for free agency after this season, was on a conference call last week with NBA commissioner Adam Silver and one of his biggest takeaways was that players – especially the ones with a chance to win a title – are eager to get back on the court as soon as possible.
"They're trying to win a championship, so I understand where they're coming from and they know everybody wants to see basketball," Thompson – a 2016 NBA champion with the Cavaliers – said from Los Angeles.
"Everybody wants to watch the playoffs. I want to watch the playoffs, with my friends, you know cheering and going crazy.
"But the main concern is just how do we do it in a way where everyone's at peace when they go to work."
