Boston Celtics rookie Robert Williams did not suit up for Saturday night's Las Vegas Summer League game against the Denver Nuggets after suffering a left knee contusion in his Celtics debut Friday night.

He played just six minutes off the bench against the 76ers before getting hit on his left knee, aggravating some lingering tendinitis. Williams was removed from the game and did not return.

The 6-10 big man told reporters after the game that he's been dealing with tendinitis "for a little bit."

"It hurt, but it's definitely something you have to go through, and I'll get more treatment back at the hotel again," Williams said Saturday morning.

Williams showed flashes of his potential Friday night against the Philadelphia 76ers, dunking off a feed from Kadeem Allen and facing up 6-11 center Norvel Pelle before knocking down a mid-range jumper. You can watch highlights of Williams' Celtics debut below.

Williams' career as a Boston Celtic got off to a rough start, sleeping through a conference call with the media the morning after the NBA draft and missing a flight to Boston and the team's first summer league practice.

After arriving in Boston to practice with his teammates, the 20-year-old Louisiana native took responsibility for missing his flight, saying "It's all on me."

Williams said he was approached by Celtics head coach Brad Stevens, who told Williams he has a once in a lifetime opportunity in front of him.

"He obviously explained to me about the opportunity," Williams said. "There's not that many so definitely a real wake-up call."

Williams, once a projected lottery pick, slipped to the Celtics at No. 27 in the draft amid concerns about his work ethic and commitment.