Celtics’ Robert Williams has a torn meniscus, and will likely miss portion of the playoffs

Robert Williams left Sunday's game in the third quarter.Jim Davis/Globe Staff

TORONTO — After climbing to the top of the NBA Eastern Conference standings, the Celtics were dealt a costly blow Monday when the team learned Robert Williams had suffered a left meniscus tear during Sunday’s 134-112 win against the Minnesota Timberwolves at TD Garden.

Hours after the team announced the injury , Celtics coach Ime Udoka said Williams will have surgery, with the club determining a variety of options. Philadelphia center Joel Embiid played through a torn meniscus last season, but the Celtics want to be cautious with Williams’s long-term future.

At minimum, Williams, a Defensive Player of the Year candidate, will miss the rest of the regular season and likely a portion of the playoffs. Udoka left open the possibility Williams could return during the postseason depending on the extent of the surgery. If Williams decides on a short-term solution, he likely would miss four to six weeks.

Udoka said backup center Daniel Theis, reacquired last month, will now play a key role in the Celtics’ defense.

Daniel Theis, seen here defending Toronto's Fred VanVleet Monday night, figures to get more minutes with Robert Williams III out.Frank Gunn/Associated Press

“It changes the dynamic obviously, how important he is for us and what he does for us,” Udoka said of Williams. “But that’s why we feel confident getting Daniel in for these reasons. As much as we wanted to shave down some minutes with Rob and Al [Horford] going into the playoffs, that’s also an insurance policy. Daniel is a guy who’s versatile, can do a lot of the same things as both of those guys.

“We’ll know more in the next few days about Rob, specifically, but until then other guys will step up and have to carry the load.”

Williams, who had averaged 10 points, 9.6 rebounds, and 2.2 blocks before his injury, brings several elements Theis doesn’t. He is one of the more athletic big men in the league and gives the Celtics easy points with lobs at the basket and is also second in the NBA in blocked shots. He was having his best season as a professional and also one of his healthiest before this injury.

“You get some of that with Daniel; he doesn’t jump as high or get up as high, but he’s a lob threat at well,” Udoka said. “He brings a different shooting touch as well. So we have Al and those guys there. But for the most part, Jayson [Tatum], Jaylen [Brown] and our guards and what they do, that will continue. We’ll have to make up some of the second-chance points. Defensively, the deterrent at the rim changes some, but Daniel brings some of the same things to the table.

“It’s going to impact us, but like I said, other guys have to step up. Nobody’s going to feel sorry, guys are capable and keep moving.”

Udoka said the team’s spirits still remain high, despite Williams’s injury.

“You keep him encouraged and we dealt with a lot of stuff injury-wise and COVID-wise early in the season,” Udoka said. “We had to play through that. Guys stepped up when Jaylen was out. We’ve been well-tested as far as going through that adversity.”

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Udoka decided to rest Tatum and Brown, who are each battling knee soreness. Instead of riding his exercise bike when he’s out of the game, Tatum was icing his right knee. Brown was flexing his leg in the fourth quarter on the Celtics bench and has been battling knee discomfort most of the season.

Ime Udoka decided to rest both Jaylen Brown and Jayson Tatum Monday night.Steven Senne/Associated Press

Horford missed his second consecutive game because of personal reasons and Udoka is unsure he will be back Wednesday against Miami. With Williams out also, the Celtics needed four new starters around Marcus Smart. Grant Williams, Aaron Nesmith, Derrick White and Theis got the nod Monday.

“Them coming in with some soreness [Sunday night]; if it would have been an easier game, [and the lead] got to the 30s, [it] would have been a possibility they would have [not] played,” Udoka said. “But a heavy load and if you look at the bigger picture of us getting healthy going toward the playoffs, that was the main goal.”

It was a critical game for the Raptors, who are fighting the Cavaliers to avoid the seventh seed and play-in tournament. The Raptors were fully healthy, with the activation of sharpshooter Gary Trent Jr., who missed the past three games with a hyperextended big toe.

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With the sudden injuries and Horford’s absence, the Celtics added depth by plucking two-way contract player Matt Ryan from G-League Maine and also signing Maine big man Juwan Morgan to a 10-day contract. The Celtics had an open roster spot.

Morgan, who had a short stint with the Utah Jazz, averaged 12.1 points, 5.5 rebounds and 34 percent 3-point shooting in 20 games with the Maine Celtics. Ryan, who played at Notre Dame, Vanderbilt and Chattanooga, averaged 19.1 points and 42 percent 3-point shooting in 27 games with Maine and Grand Rapids. He will wear No. 37. Morgan will wear No. 4.

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Tatum was named Eastern Conference Player of the Week for the second consecutive week and the third time this month, likely guaranteeing he’ll be Player of the Month next week. Tatum averaged 32 points and 58.2 percent shooting in three games, all wins.