Celtics rookie Robert Williams, who overslept and missed a conference call with the media the day after the NBA draft, missed a flight to Boston and was absent from the team's first summer league practice on Sunday.

Williams, a projected lottery pick, slipped to the Celtics at No. 27. Questions about his commitment and work ethic contributed to his draft night slide.

The 20-year-old big man went back home after the Celtics introduced him at a news conference Friday morning. According to Celtics PR, Williams missed a flight back to Boston and was not at Sunday's practice.

"I think everyone's disappointed," said Celtics assistant coach Jay Larranaga, who will serve as head coach of the Celtics’ Las Vegas Summer League team. "You want to get everything off to a good start in the first day, but we'll handle that internally and move forward."

Williams declined an offer to attend the NBA draft in Brooklyn, opting instead to gather with family at a Buffalo Wild Wings in his home state of Louisiana. Williams admitted he missed the conference call the next morning because he overslept.