Zion Williamson had surgery Monday to repair a torn meniscus in his right knee and is expected to miss six to eight weeks, the New Orleans Pelicans announced.

Coach Alvin Gentry said on Friday that he believed Williamson suffered the knee injury during the Pelicans' preseason game against the San Antonio Spurs last Sunday.

Williamson, the No. 1 overall pick out of Duke, was averaging 23.3 points and 6.5 rebounds while shooting 71.4% in the Pelicans' first four preseason games and averaging 27.3 minutes.

The 6-foot-7, 284-pound Williamson missed time in summer league after he banged his left knee in a collision with another player. After just eight minutes, the Pelicans shut Williamson down for the summer, although they said they were just being overly cautious.

Williamson suffered a mild right knee sprain during his only season at Duke. That injury occurred when his sneaker gave out just seconds into a game against North Carolina. He missed three weeks with the injury before returning in the ACC tournament.

Without Williamson on the floor, the Pelicans will likely turn to another rookie -- albeit a much older one -- to fill his minutes. Nicolo Melli, a 28-year-old Italian player, came to New Orleans this summer after a professional career that started in 2007 overseas.

He has played as Williamson's backup this preseason and has averaged 8.8 points and 6.0 rebounds in 17.0 minutes per game. His rebounding average is second on the team to Williamson's through four preseason games.

ESPN's Andrew Lopez contributed to this report.