Boston’s Al Horford will miss the rest of the preseason after testing positive for COVID-19, the team announced Tuesday. Charles Krupa/Associated Press

The Celtics will be without Al Horford for at least the remainder of their preseason schedule after the veteran big man tested positive for COVID-19 on Tuesday. The team announced Horford is currently isolating away from the team.

Horford is the second Celtic to test positive for COVID-19 in the past week after All-Star forward Jaylen Brown did so on Friday. Brown did not make the trip as Boston flew to Florida on Monday ahead of their two preseason matchups with the Orlando Magic and Miami Heat this week. It is not clear if Horford made the trip with his teammates before testing positive.

The 35-year-old Horford had been in the midst of a standout preseason for Boston after being acquired in a trade from the Oklahoma City Thunder in June.

“He does (look fresh),” Ime Udoka said during training camp. “It’s noticeable. Whether he found the fountain of youth or it’s just the time off that he got not playing all the games last year in Oklahoma City. I mentioned having him in Philadelphia where he sat out some games here and there, but for the most part, he’s come back in shape.

“He’s looked great since the day he came into training camp and talked about how he took care of his body and how much of an opportunity this is. And he’s happy to be back. So you can see with his body and how he’s playing, he looks lively, fresh, and looks rejuvenated. We’re loving what we’re seeing from him.”

Udoka was hopeful ahead of Saturday’s win over the Raptors that the Celtics would be able to avoid any more positive COVID-19 cases after Brown tested positive.

“It’s always a concern, but we have the proper testing protocols in place and everybody’s getting checked out,” Udoka said. “So far so good, as was the case with me; it didn’t affect anybody else overall, and I was around the guys for a little bit before I found out. So we’re hoping it stays with that. Like I said, we’ve been more vigorous with the testing the last few days, and everybody’s coming out clean.”

The Celtics play their regular season opener against the New York Knicks on Oct. 20 at Madison Square Garden. Brown is expected to be back in time for the opener but Horford may not be cleared from NBA health and safety protocols in time to suit up.

NETS: Kyrie Irving can continue to choose not to be vaccinated for COVID-19.

He just won’t play for the Brooklyn Nets until he is.

The Nets announced that Irving would not play or practice with them until he could be a full participant, ending the idea that he would play in only road games.

Irving hasn’t said he isn’t vaccinated, asking for privacy when he spoke via Zoom during the team’s media day on Sept. 27.

But he had rarely been with the team in New York, where a mandate requires professional athletes playing for a team in the city have to be vaccinated against COVID-19 to play or practice in public venues.

“Kyrie’s made it clear that he has a choice in this matter and it’s ultimately going to be up to him what he decides,” Nets General Manager Sean Marks said. “We respect the fact that he has a choice, he can make his own and right now what’s best for the organization is the path that we’re taking.”

Teams aren’t allowed to reveal private details of players’ health. But asked Tuesday if Irving was vaccinated, Marks said: “If he was vaccinated, we wouldn’t be having this discussion. I think that’s probably pretty clear.”

Marks said he and owner Joe Tsai together made the decision, adding that it came through discussions with Irving and his associates.

“Kyrie loves to play basketball, wants to be out there, wants to be participating with his teammates,” Marks said. “But again, this is a choice that Kyrie had and he was well aware of that.”

Irving wasn’t even eligible to practice with the Nets in New York until Friday, when the city told the team that its training facility was considered a private venue.

Irving then joined the team at an outdoor practice Saturday and worked out with the team Sunday, but didn’t play in Brooklyn’s exhibition game at Philadelphia on Monday.

Coach Steve Nash had said that the Nets knew they were going to be missing Irving for some games. For now, at least, it will be all of them.

With Kevin Durant, James Harden and Irving, the Nets were considered a favorite to win the NBA title. They were eliminated by the Milwaukee Bucks in the second round of last season’s playoffs after Irving sprained his ankle and missed the final three games.

NBA players are not required to be vaccinated, but they face more testing and restrictions on their ability to be around their teammates. The league had said that players wouldn’t be paid for games they miss because they are ineligible to play.

Marks said Irving would still be paid for road games.

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