The Boston Celtics were just hit with a brutal injury update ahead of their Eastern Conference Finals series opener against the Miami Heat on Tuesday. According to Shams Charania, both Marcus Smart and Al Horford will be unavailable for Game 1 in Miami.

As Charania denotes, Horford is currently in health and safety protocols, though it's unclear when exactly he entered the league's COVID protocols.

As for Smart, the Celtics point guard and reigning Defensive Player of the Year suffered a foot sprain in Game 7 against the Bucks, which is going to keep him sidelined against the Heat in Tuesday night's series opener.

This is a significant loss for the Celtics, particularly on defense. Horford had been playing elite defense all series against Milwaukee, so not having him available in the paint is a big loss, especially with Robert Williams not quite at 100%. Smart's defensive prowess goes without saying, and not having him there to pressure the Heat's ball handlers will be a big loss.

Smart's absence will open the door for increased minutes for Derrick White and Payton Pritchard, while Daniel Theis figures to log some more run in Horford's stead.

During the 2022 playoffs, Horford has averaged 13.0 points, 9.4 rebounds, 3.4 assists, and is shooting 45.1% from beyond the arc. Smart, on the other hand, was averaging 15.0 points, 6.2 assists, and 1.1 steals per game, shooting 35.4% from 3-point range.

Tip-off for Game 1 is set for 8:30 p.m. ET, at which point the top two teams in the Eastern Conference will square off, though Boston will be down a couple of key players for the opener.