Portland Trail Blazers center Robert Williams III will require right knee surgery and is expected to be sidelined for an extended period of time, sources told ESPN on Monday.

Doctors and Williams' agent Kevin Bradbury of Lift Sports Management are working to gather information and discussing the kind of surgery that'll be necessary and how long of a timeline will be required for recovery, sources said.

Williams injured the knee in Sunday night's loss to the Memphis Grizzlies and he underwent imaging on Monday.

Williams arrived as part of the Jrue Holiday trade with the Boston Celtics in September, and had been a trade target of a number of teams who hoped that the Blazers would consider moving him before the February trade deadline.

Portland had been playing Williams along with Deandre Ayton, who arrived from Phoenix as part of the Damian Lillard trade.

Williams, 26, has shown himself to be one of the league's elite rim protectors, leading the NBA in field goal percentage allowed as the closest defender among players to defend 1,000 shots, per Second Spectrum.

Williams missed the start of the 2022-2023 season for the Celtics after undergoing offseason surgery on his left knee. He also tore the meniscus in his left knee in March of 2022.

A second-team All-NBA defensive selection in 2022, Williams had his best season that year as the Celtics made a run to the NBA Finals. He started 61 games, averaging 10 points, 9 rebounds and 2 blocks a game.