The Boston Celtics had both Al Horford and Marcus Smart back

The Boston Celtics had both Al Horford and Marcus Smart back in the starting lineup for Game 2 of the Eastern Conference finals on Thursday against the Miami Heat.

Horford, who abruptly went into the NBA's health and safety protocols a couple of hours before Boston's 118-107 Game 1 loss on Tuesday, was upgraded to doubtful Wednesday evening and then was rapidly upgraded from questionable to available in the span of about 90 minutes Thursday.

Smart, who missed Game 1 because of a midfoot sprain that he suffered in Game 7 against the Milwaukee Bucks, was listed as probable to play. Celtics coach Ime Udoka confirmed that both players will play in Thursday's game and are a "full go" from a minutes standpoint.

"[Horford] passed all the protocols, passed all the tests," Udoka said. "I'm not a doctor, but he had to pass a certain amount of tests and you know, league protocols, and so he did and he was feeling fine from the get-go. Happy to have him back."

However, in a memo dated April 30 and obtained by ESPN, the league added a third game-day testing mechanism to potentially allow for players to return the day of a game.

In that circumstance, a player could return to team activities if he returns two consecutive "not detected" results from PCR tests collected on game day.

If either PCR test returns a positive or inconclusive test result, this protocol shall not apply, and the player must remain in isolation.

The Celtics also announced that Derrick White would miss Game 2 for personal reasons, as he and his wife are expecting a child.

"Derrick is having a baby," Udoka said. "It came sooner than expected. But we support our guys always in that situation. He had to rush home today."

White started Game 1 in place of Smart and finished with three points and four assists in 29 minutes. He is expected to be back with the team for Game 3 on Saturday night when the series shifts back to Boston.