Jayson Tatum gets helped off the court after rupturing his Achilles late in Monday night's playoff game in New York. (AP photo)

BOSTON (AP) — Boston Celtics star Jayson Tatum had surgery Tuesday to repair a ruptured right Achilles tendon that will sideline him for the remainder of the playoffs, the team announced.

The Celtics announced the extent of Tatum’s injury and the surgery a day after the six-time All-Star went down in the Celtics’ 121-113 Game 4 loss to the New York Knicks, putting both the hopes of the defending champions repeating and Tatum’s playing status for next season in doubt.

They did not give a timetable for his return but said a full recovery was expected.

When Kevin Durant tore his Achilles tendon during the 2019 NBA Finals, he wound up missing the entire 2019-2020 season.

The 27-year-old Tatum is leading the Celtics in points (28.1), rebounds (11.5) and assists (5.4) per game for the second straight postseason.

The Knicks lead the Celtics 3-1 in their Eastern Conference semifinals series. Game 5 is in Boston on Wednesday night.

HOW THE KNICKS TOOK CONTROL

Jalen Brunson and the New York Knicks had just taken control of the game with another fourth-quarter kick when Jayson Tatum fell to the court with what figurd to be potentially severe right leg injury.

At the time, the specifics of Tatum’s injury are uncertain but the situation in the Eastern Conference semifinals is clear.

The Knicks need one more victory to reach the conference finals for the first time in 25 years. The Celtics need to match the biggest comeback in NBA history to extend their title reign.

Brunson had 39 points and 12 assists, and the Knicks pushed the defending champions to the brink of elimination with a 121-113 victory Monday night in Game 4.

Blown out in Game 3, the Knicks dominated the second half to become the first home team to win in this series.

“I think it was a sense of urgency, desperation, just knowing that we have a great opportunity,” Brunson said.

The Celtics will have to make the NBA’s 14th comeback from a 3-1 deficit and may have to do it without Tatum, who was carried off the court with a right leg injury with 2:58 left.

Mikal Bridges and Karl-Anthony Towns each added 23 points and OG Anunoby bounced back from two poor performances by scoring 20 for the Knicks, who can win the series Wednesday night at Boston. If not, they would come back to Madison Square Garden to try to do it Friday night.

“We have to turn that page quickly and do our first job, which is win on Wednesday. That’s the mindset,” Celtics veteran Al Horford said. “As a group, we just have to rally together because obviously we’ve lost our leader, the guy that gets us going.”

Tatum scored 42 points, his high in these playoffs, before he was hurt when the Celtics turned the ball over and his leg gave out as he tried to lunge forward toward the loose ball.

Nobody has come from 3-1 down since Denver did it twice in 2020 at the Walt Disney World resort. It hasn’t happened when a team had to win a true road game since Cleveland rallied past Golden State in the 2016 NBA Finals.

After leading by at least 20 points in the first three games — but blowing the first two of them in Boston — the Celtics had another double-digit lead less than five minutes into this game and were up 62-51 at halftime.

Brunson then scored 18 in a desperate third quarter, when the Knicks played their starters the entire way and outscored the Celtics 37-23 to set up a thrilling final period.

“Just keep fighting,” Bridges said. “We were down way worse before.”

Tatum’s three-point play tied it for the final time at 102-all before Anunoby hit a 3-pointer and the Knicks later put it away for good with an 11-0 burst that made it 116-104.

Derrick White made six 3-pointers and scored 23 points for the Celtics. Jaylen Brown had 20.