Celtics' Marcus Smart, Al Horford out for Game 1 of Eastern Conference finals

The Boston Celtics will be without Marcus Smart and Al Horford on Tuesday night.

The Celtics announced that Smart and Horford will miss Game 1 of the Eastern Conference finals against the Miami Heat. Smart is out with a right mid-foot sprain, and Horford has entered the NBA's COVID-19 health and safety protocols.

It’s unclear if Horford is experiencing coronavirus-related symptoms, or how long he will be sidelined. The team is reportedly prepared for Horford to miss Game 2 of the series, too. The 35-year-old has averaged 13 points and 9.4 rebounds per game throughout the postseason, and put up 30 points in their Game 4 win over the Milwaukee Bucks earlier this month.

Smart first injured his foot in Game 7 against the Bucks, and has been listed as questionable for Game 1. He underwent an MRI on Monday, though it came back clean. The NBA’s Defensive Player of the Year has averaged 15 points and 6.2 assists so far this postseason.

"Yes he's still pretty sore," Celtics coach Ime Udoka said earlier Tuesday before he was ruled out. "He tested out a little bit here and we're hoping he's feeling better, but there's some soreness there, some swelling still, and we'll monitor him throughout the day, get some treatment, and he'll still be listed as questionable … We’re hoping he has some good treatment today, and we’ll see how it goes.”

It’s unclear how long Smart will be out with the foot sprain.

Though those two won't be able to play on Tuesday, Celtics big man Robert Williams "should be able to play significant minutes" after dealing with a lingering knee injury, according to ESPN's Adrian Wojnarowski. Williams hasn’t played since Game 3 of their second-round series against the Bucks, though he was available for Game 7 “if needed.” He’s reportedly had a good few days of practice, and should be good to go in Horford’s absence.

Game 2 of the series is set for Thursday night.

Boston Celtics' Marcus Smart
Marcus Smart and Al Horford are both out for Game 1 of the Eastern Conference finals. (AP/Morry Gash)