Pelicans head coach Alvin Gentry isn't worried about Zion Williamson falling behind while he recovers from injury. (0:54)

New Orleans Pelicans rookie Zion Williamson has avoided a severe injury to his right knee but is expected to miss a period of weeks to start the regular season, sources told ESPN's Adrian Wojnarowski on Friday.

Williamson did not travel with the team to New York for Friday's preseason game against the Knicks and instead stayed back in New Orleans for further testing.

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

"Yeah I mean he's fine," Gentry told reporters when asked how Williamson was feeling. "He's not dead guys. He's a typical 19-year-old kid. He's upbeat, he has fun and he's living his dream as he said."

The injury puts a damper on what had been an excellent preseason for the No. 1 overall pick. Williamson 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.

Now New Orleans heads into the season with its star rookie on the sideline.

The Pelicans figure to be cautious regarding Williamson's return, but the team is confident he will make a full recovery. 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.

He was the prohibitive favorite for the NBA's Rookie of the Year award, coming in at -250 odds at Caesars Sportsbook.

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.

The injury could also open up time for the Pelicans to play Kenrich Williams at power forward. Williams is third on the team with 4.8 rebounds per game in the preseason. It's also possible the Pelicans could play Brandon Ingram at the 4 spot in spurts.

New Orleans has Derrick Favors slated to start at center, with Jahlil Okafor and Jaxson Hayes backing him up.

At shootaround Friday morning, Jrue Holiday said he had not spoken with Williamson and had only just found out about the injury when he got a Twitter notification on his Apple Watch. Holiday's advice to Williamson: "Stay strong."

"Obviously, his body is strong," Holiday said. "Your body can bounce back. But mentally, I think that's where you just have to lock in and be patient."

Information from ESPN's Malika Andrews was used in this report.