The Wizards announced Tuesday that Wall would have the operation in Cleveland and that a timeline for his return would be determined afterward.
A person with direct knowledge of the injury said Wall could miss six to eight weeks. That person spoke to The Associated Press on condition of anonymity because the team did not release any estimate of the length of Wall's absence. Washington's last regular-season game is April 11.
"It just proves that he wasn't the John that we know," backup guard Tomas Satoransky said. "His knee was bothering him all season long."
This is the latest knee problem for the No. 1 overall pick in the 2010 NBA draft out of Kentucky. Wall had surgery on both of his knees before last season.
"It's definitely not an easy day," Brooks said at his pregame session with the media. "Over the last week, we saw he was dragging a little bit. ... Decided going forward that it would be best for him to get a little cleanout."
Wall is second on the Wizards in scoring, averaging 19.4 points, and is second in the league with 9.3 assists per game. In July, he agreed to a $170 million, four-year contract extension that starts next season.
He was selected last week for his fifth NBA All-Star Game but will miss that event in Los Angeles next month. Commissioner Adam Silver chose Detroit Pistons center Andre Drummond to replace Wall on LeBron James' team.
The Wizards entered Tuesday tied for fifth in the Eastern Conference with a 27-22 record.
"We don't have the cushion that John can take over a game," Brooks said, "or John can create a shot (for himself) or ... for the other guys."
Washington went into Tuesday 6-6 without Wall this season.
The timing of the surgery gives Wizards President Ernie Grunfeld a chance to find a new point guard before the NBA trading deadline, which is Feb. 8.
Brooks said he didn't think Wall's injury will substantially alter the team's approach to the deadline.
"This is a minor setback. And he will be back — I don't know when," Brooks said. "We're not going to change things up just 'cause of this."
Reserves Satoransky and Tim Frazier figure to get additional playing time.
"We cannot panic about it," Satoransky said about losing Wall.
"John is the main guy, so it's always tough to cover your main guy when he goes down," said Satoransky, who is averaging five points and 2.6 assists. "It's very challenging."
Wall sat out Washington's most recent game, at Atlanta on Saturday, because of a recurrence of soreness and swelling in his left knee. Earlier issues led him to sit out nine games in November and December, and attempts to help him included draining the knee and getting platelet-rich plasma injections.
"It just kept becoming a problem," Brooks said.
Led by its backcourt of Wall and Bradley Beal , a first-time All-Star pick this season, Washington reached the Eastern Conference semifinals each of the past two years before being eliminated from the playoffs.
Now they'll have to try to go what could be a long stretch without their on-court leader.
"By the time he comes back, we'll be in the playoff push," forward Markieff Morris said, "or just getting ready for the playoffs."
AP Sports Writer Tom Withers in Cleveland and freelance writer Ben Standig in Washington contributed to this report.
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