Kristaps Porzingis’ lingering illness sidelined him for the seventh straight game Wednesday night.

After initially listing the center as questionable, the Celtics downgraded Porzingis to out for their matchup with the Oklahoma City Thunder at TD Garden.

Jayson Tatum (listed as questionable) and Jaylen Brown (probable) both were upgraded to available for Boston.

Porzingis has played in just one of the Celtics’ last nine games. He posted a health update on social media Monday night, saying he has “been dealing with some viral illness that we haven’t been able to fully identify yet.”

That illness has not kept Porzingis away from the team. He’s been a regular visitor to the Celtics’ facilities, attending Wednesday’s morning shootaround and making an appearance in the locker room before the game against OKC.

“I think at the end of the day, just making sure he’s safe,” Celtics head coach Joe Mazzulla said after Monday’s win over Utah. “He’s still able to come in and be around the guys as best he can. Trying to stay in the best shape possible. He’s been on the court. He’s doing what he can to get back. But he kind of said it best. At the same time, we’ve just got to kind of make sure he’s good, and we do what’s best for him.”

Thunder head coach Mark Daigneault said the Celtics are a “significantly” different team when Porzingis is not available — no other Boston big can replicate his combination of 3-point shooting and top-tier rim defense — but still a formidable foe because of their depth and versatility.

“When he’s out there, that certainly changes the dynamic of how they attack and how they play and what they’re capable of,” Daigneault said. “But that opens up more space. They’re a great team, and usually when you open up more space, more opportunity on a great team, there’s guys that can step in, and I think you’ve seen that all season. Boston is always missing one guy, it almost seems like, and yet these other guys step in there with a lot of confidence. … So it definitely changes them, but it doesn’t make them any less dangerous.”

OKC also was missing two key players for the potential NBA Finals preview. All-Star forward Jalen Williams missed the game with a hip injury, and two-time All-Defensive selection Alex Caruso was downgraded to out due to illness.