Robert Williams’ professional career is not off to a great start.

The 20-year-old rookie missed the Celtics' first summer league practice Sunday after he failed to make his flight to Boston, according to multiple reports. Williams overslept an introductory conference call following the draft last month.

The Celtics selected Williams with the 27th overall pick in the 2018 NBA Draft. He averaged 10.4 points and 9.2 rebounds per game as a sophomore on a Texas A&M team that went 22-13 last season.

Williams told the Boston Globe earlier this week he was excited to join the Celtics.

“As I said from the beginning, it’s a great fit,” Williams said. “I’m coming into a team that’s competing to be in the Finals. It’s a blessing. With the fans and city behind them, it makes it 10 times better. I feel like I fell in a great place.”

Williams was suspended by Texas A&M for the first two games of 2017-18 after he violated a university policy.