Robert Williams and the Celtics have reportedly agreed on a four-year extension worth $54 million. Michael Dwyer/Associated Press

The Boston Celtics have agreed to a four-year extension worth $54 million with center Robert Williams, according to multiple reports.

The deal will take effect during the 2022-23 season. Williams, 23, moved into the starting lineup at center last season after the team traded away Daniel Theis. He averaged a career-high 8.0 points, 6.9 rebounds, 1.8 assists and 1.8 blocks in 18.9 minutes per game.

The biggest concern for the Celtics involving Williams is his durability, as he has played just 113 games during three seasons after being drafted No. 27 overall in 2018.

Boston previously agreed on a four-year deal with Marcus Smart on Monday. Those contracts will eat up the majority of the team’s cap room heading into the 2022 free agency, meaning any top-tier target for the Celtics in the next offseason or two will need to be acquired via trade.

KEVIN GARNETT, who played in Boston from 2007-13 and won the 2008 NBA championship, will have his No. 5 retired on March 13 during a game against the Dallas Mavericks.

Garnett’s No. 5 was supposed to be retired during the 2020-21 season, but the ceremony was pushed back because of the pandemic. TD Garden should be at or near full capacity this fall as the Celtics look to honor Garnett in front of fans.

Garnett was a crucial figure in bringing Boston its 17th championship banner, joining forces with longtime franchise legend Paul Pierce and another important piece in Ray Allen. He averaged 15.7 points and 8.3 rebounds in his 396 games as a Celtic. While his best play came in a Minnesota uniform, including winning the 2004 NBA MVP, he reached the pinnacle of the sport when he helped the Celtics beat the Lakers in the 2008 NBA finals.

Garnett was inducted into the Naismith Memorial Hall of Fame earlier this year as part of the Class of 2020. The enshrinement ceremony was supposed to be last year but was pushed back because of the pandemic.

BRAD STEVENS confirmed that Boston’s last two second-round picks – Yam Madar and Juhann Begarin – will play overseas for at least another season.

It was the most likely path with the Celtics’ roster limitations; it was all but confirmed once Madar signed with Partizan Belgrade in Serbia for next season. But that doesn’t mean they’ll be stashed away long.

“They both have their teams and where they will be and we think they’re really good situations,” Stevens said. “We think they’re going to do great. We’re going to be over there quite a bit. I think they’re both guys that you can see being really impactful sooner rather than later. Both guys that we’re excited about.”