Boston Celtics center Robert Williams will reportedly undergo an arthroscopic procedure on his left knee that will require four-to-six weeks of recovery, according to Sean Deveney of Heavy.com.

Williams is expected to have the procedure at some point this week, per Deveney.

The Celtics begin their regular season on Oct. 18, exactly four weeks from Tuesday.

The 24-year-old also underwent knee surgery in March, which limited him throughout the team's playoff run to the NBA Finals.

Williams was initially diagnosed with a torn meniscus, which cost him the final seven games of the regular season, but he returned in the playoffs after less than a month off the court. He ended up missing seven games during the postseason run, but the team was confident he would return to full strength by the start of the 2022-23 campaign.

"There is no long-term concern about his knee injury," Brian Robb of Mass Live reported. "No surgery was needed so ample rest this summer should have him at 100 percent in camp."

The latest issue now raises question marks heading into a season where the Celtics have high expectations.

Williams is coming off his best season in the NBA, averaging 10.0 points, 9.6 rebounds and 2.2 blocks per game while shooting 73.6 percent from the field. He became a full-time starter in his fourth season in Boston, and rewarded the coaching staff with a team-high 9.9 win shares, per Basketball Reference, seventh-best in the league.

Losing the top rim-protector for an extended stretch would be damaging for Boston as it battles for seeding with the top teams in the Eastern Conference.

Veteran Al Horford will become even more important in the early part of the season, while Luke Kornet and Grant Williams will likely also see extra minutes at center.