The Boston Celtics suspended guard Marcus Smart for Friday's preseason finale in Miami against the Heat because he missed the team's flight to Florida earlier this week, a source told ESPN's Adrian Wojnarowski.

"We're going to keep that in-house," Smart said Thursday afternoon after practice in Miami. "It's over and done with. We're excited for the game at MSG, though."

The Celtics, already without Jaylen Brown and Al Horford after they tested positive for COVID-19, also sat Smart, Jayson Tatum, Dennis Schroder and Josh Richardson for Wednesday's 103-102 loss in Orlando to the Magic. The plan had been for the Celtics to play their regular players close to regular minutes Friday before they open the regular season Wednesday at Madison Square Garden against former teammate Kemba Walker and the New York Knicks.

"It's internal," Celtics coach Ime Udoka said. "We've handled it. He's remorseful, and we hold Marcus to a high standard. We've made it clear from Day 1, so he'll obviously be out tomorrow night. He's with us here on the trip. Just look forward to moving on from this growing and obviously abiding by the team rules and principles.

"Marcus is one of our leaders that we expect a lot from. He understands that. He's remorseful, and we'll move on from there."

Smart, who signed a four-year, $77 million extension to remain with the Celtics -- the only team he's played for since being drafted sixth overall in 2014 -- after setting career-high averages in points (13.1), assists (5.7) and minutes (32.9) last season. He enters this season as Boston's starting point guard after the Celtics traded Walker in the offseason.

But with Smart and backup Payton Pritchard, who injured his nose in Wednesday's game, out Friday, along with Brown and Horford, Udoka won't get anything close to a look at his full roster.

"We won't get to see certain lineups that we obviously wanted to see, but we have to move along," Udoka said. "We've done that with Al and Jaylen out as well. So we just had a nice practice, added some new things for tomorrow and the week going forward, and we'll keep it moving. Guys will have the opportunity, and then Marcus and others will catch up when they come back in the next week or so."

The Celtics are optimistic Brown will be out of the NBA's health and safety protocols in time to play against the Knicks. Horford's timeline, however, is a lot tighter.