Joe Mazzulla reveals the Celtics starters’ plan in Game 4 of the preseason

After playing most of his regular starters in the Celtics’ first three preseason games, head coach Joe Mazzulla gave his top unit a night off Sunday.

Mazzulla announced in his pregame press conference that Jayson Tatum, Jaylen Brown, Jrue Holiday, Derrick White and Luke Kornet would not play against the Toronto Raptors at TD Garden.

Those five started both of Boston’s games in Abu Dhabi and Saturday night’s 50-point home win over the Philadelphia 76ers.

Veteran center Al Horford also sat out Sunday for the fourth straight game. Mazzulla plans to give Horford minutes on Tuesday when the Celtics close out their preseason in Toronto.

“He’s going to play Tuesday. He’s good,” Mazzulla said of the 38-year-old, who is entering his 18th NBA season. “He’s ready to go. He’s stepping up, getting in shape, working hard. He’ll play Tuesday in Toronto.”

Kristaps Porzingis was also sidelined as he recovers from offseason leg surgery. Boston’s starting center, who has watched from the bench in street clothes this preseason, is targeting a return in December.

Mazzulla said all other Celtics players would be available Sunday. Several members of that group are fighting for rotation roles and roster spots with just over a week until the start of the regular season.

Among those hopefuls: second-year pro Jordan Walsh, first-round rookie Baylor Scheierman and veteran newcomer Lonnie Walker IV, who is with the Celtics on a training camp tryout deal.

“The message is the same no matter who’s playing,” Mazzulla said. “We will compete at a high level. Let’s run. We’re going to stick to things and run our system offensively and defensively and make sure we play hard. The message is always the same, regardless of who’s in, who’s out, and I think that’s the reason we have the continuity that we do, because of that standard. So it’s the same.”