While the Celtics expect to have Jaylen Brown back before the regular-season opener, it’s looking increasingly likely they won’t be at full strength by then.

Al Horford hit the injury report Tuesday because of health and safety protocols; the team announced he tested positive for COVID-19. Considering the 10-day quarantine rules, Boston Coach Ime Udoka said Wednesday that “it’s going to be very close” on whether Horford will be back by the Oct. 20 game against the Knicks.

“Al’s doing OK,” Udoka said. “Obviously, nobody wants to be in this situation, so there’s no real positive about it. But healthwise overall, he’s doing OK.”

Udoka said Horford tested positive for COVID-19 on Monday, ahead of the team’s Florida road trip this week. Ten days after Monday translates to Oct. 21, which means Horford is unlikely to suit up for the regular-season opener. The Celtics have their home opener on Oct. 22 against the Raptors.

The news about Horford is blow for the Celtics, who lost more than 160 players days to the virus last season. Between injuries and COVID-19, the team has had a string of unfortunate luck brought upon by the pandemic.

Udoka said there were some small positives with guys being out because of the virus, but it wasn’t much. While the Celtics are missing players during the preseason, it still disrupts the ramp-up period where guys want to jell and create some chemistry.

“I’ve seen the number of games missed last year,” Udoka said. “Really hit us hard last year, and so I knew that coming in. Obviously, it is a frustrating thing. And being that I dealt with it as well right before, I guess the silver lining is that when it’s happening, if there is one, in the preseason.”

• The Celtics played without Jayson Tatum, Jaylen Brown, Al Horford, Josh Richardson, Marcus Smart, Dennis Schroder on Wednesday night in their second tuneup against the Orlando Magic this preseason and came up just short, falling 103-102 at Amway Arena.

Aaron Nesmith led Boston with 23 points.

76ERS: This much is known: Ben Simmons is back in Philadelphia. But there’s no clear sign yet the All-Star guard is set to rescind his trade request and actually play for the 76ers.

Even Coach Doc Rivers – publicly, at least – says he’s unsure of the status of the trade demand, the latest wrinkle in the on-again-off-again relationship between Simmons and the Sixers.

“I don’t know. He’s voiced that, but we’ll see how that works out,” Rivers said Wednesday at team practice.

A rescinded request seems improbable, though Rivers said Simmons “was great, he was good” when the two met on Tuesday, a day after the three-time All-Star surprised the franchise by showing up to its arena during a preseason game to take a COVID-19 test.

Rivers said Simmons was scheduled to return to the practice facility late Wednesday for an individual workout and will not practice with the team until he clears NBA health and safety protocols.

That is, if Simmons returns to play at all.

That’s still a big if for the Sixers, especially with one more preseason game Friday at Detroit before next week’s season opener at New Orleans. Much like Marshawn Lynch at a Super Bowl media day, Simmons may be here only so he won’t get fined. The 25-year-old from Australia has four years and $147 million left on his max contract – though the 76ers placed in escrow $8.25 million due to the guard, and fines for missing games and practices could be subtracted from that amount.

Rivers, who turned 60 on Wednesday, said he wanted Simmons to play.

“I’m assuming he’s going to play, but who knows? I can’t get in anyone’s head,” Rivers said.

Rivers said he hasn’t ruled out Simmons traveling with the team to Detroit.

“Whether we play him or not, that’s going to depend on what we see this week,” Rivers said. “He’s coming from behind, because he hasn’t been in camp, obviously. Having said that, do you rush him and put him on the floor? That’s a whole other subject. What we see this week is how we determine everything going forward.”

Simmons missed training camp and the preseason so far in the wake of his offseason trade demand that rankled some teammates, raised the wrath of fans and left many puzzled why he wants off last season’s No. 1 seed in the Eastern Conference.

Sixers President Daryl Morey and Rivers have been publicly optimistic since the start of training camp that Simmons would play again for the Sixers.

Simmons, the No. 1 pick of the 2016 draft, had been paired with Joel Embiid as the franchise cornerstones as the Sixers chase their first NBA championship since 1983. He averaged 15.9 points, 8.1 rebounds and 7.7 assists over four seasons with the Sixers, who drafted him out of LSU, where he played only one season.