The Boston Celtics and center Robert Williams have agreed to a four-year, $54 million contract extension, agent Kevin Bradbury of REP1 Sports told ESPN's Adrian Wojnarowski on Friday.

Source: Adrian Wojnarowski and Tim Bontemps/ESPN

ANALYSIS: Williams started 13 of 52 games played for the Celtics last season. The 23-year-old center averaged 8.0 points, 6.9 rebounds and 1.8 blocks per game in 2020-21 and has made 72% of his career field goal attempts. He joins Marcus Smart as Celtics players to extend their contracts in the past week.