Boston Celtics' Marcus Smart (midfoot sprain) probable, Al Horford (health and safety protocols) doubtful for Game 2 against Miami Heat

MIAMI -- The Boston Celtics said Marcus Smart is probable to play in Game 2 of the Eastern Conference finals Thursday night with a right midfoot sprain, and Al Horford is doubtful as he remains in the NBA's health and safety protocols.

Both players missed Boston's Game 1 loss Tuesday against the Miami Heat. Smart had been questionable to play all day leading up to the game after taking a hard fall in Boston's Game 7 victory over the Milwaukee Bucks in the Eastern Conference semifinals that allowed them to advance to reach the East finals for a fourth time in six years.

Horford's absence, however, came as a surprise, one the team didn't know it would be dealing with until a couple of hours before the game.

"We've got to be even more disciplined," Jaylen Brown said after that Game 1 loss. "Obviously, we weren't prepared to be without Al. We definitely weren't prepared to be without Al and Smart. It's not an excuse. We've got to be better."

While Smart's absence wasn't expected to be long-term, Horford's return to play timeline is unclear. For a player to return to game action after testing positive, there are two paths: Return two consecutive negative PCR tests at least 24 hours apart or return two consecutive PCR tests sampled at least 24 hours apart with cycle threshold (CT) values greater than 30 beginning no sooner than Day 4 and 5 after initially testing positive.

This marks the third time Horford has been placed in the league's health and safety protocols. He tested positive for COVID-19 during the preseason, and then was placed in the protocols again in December.

Also on Wednesday, Boston coach Ime Udoka was sick with a non-COVID-19 illness.

Celtics center Robert Williams, who returned to the starting lineup and played 28 minutes in Game 1, said he felt fine Wednesday after sitting out Games 5, 6 and 7 against Milwaukee with a bone bruise in his left knee -- the same knee which he had surgery on his meniscus late in the regular season and missed the beginning of the playoffs.

Asked about a moment when he came up limping in the fourth quarter, grabbing at that leg, Williams said it was just a case of cramps, and that he would be fine for Game 2.

The Heat once again said Kyle Lowry is out for Game 2 with a hamstring injury, marking the fourth straight game he'll have missed, and the eighth he'll have sat out so far in these playoffs.