KANSAS CITY, Mo. -- Defensive back Tyrann Mathieu has been a constant in the Kansas City Chiefs defense in every meaningful game since he signed as a free agent in 2019, helping his team to back to back Super Bowl appearances.

So even the Chiefs are unsure of what to expect in Sunday's season opener against the Cleveland Browns (4:25 p.m. ET, CBS) if Mathieu doesn't play. After a recent positive test, Mathieu remains on the COVID-19 list and hasn't practiced this week. The Chiefs are holding out some hope he could play.

"It's up in the air and it's a little bit challenging to game plan for," defensive coordinator Steve Spagnuolo said. "We've got Plan A and Plan B.

"We'll move guys around, do what we have to, try to do most of the things we do with Tyrann but certainly some of those things are going to change and some of the calls might alter because of that."

Part of the trouble with replacing Mathieu is his versatility. He serves a lot of roles for the Chiefs, playing not only as a safety but also in slot coverage and occasionally lining up as a linebacker.

He has missed one game since joining the Chiefs, that being Week 17 last year against the Los Angeles Chargers when the Chiefs had secured the No. 1 overall playoff seed and rested as many of their regulars as possible.

Mathieu had an interception in last season's 22-17 divisional round playoff win over the Browns.

As for what's reasonable to expect from Mathieu on Sunday if he plays after missing so much practice time, Spagnuolo said, "We don't know. But this dude is a special guy, in my opinion. We'll see. I think we've got to be fair to him. We always say that sometimes you've got to protect the players from themselves so we've got to be careful there."

Spagnuolo said Mathieu has been involved in the Chiefs' defensive meetings virtually.

"Thank God we're way ahead in this whole Zoom thing," he said. "Otherwise we'd be trying to figure out [how to coach him]. The camera sits right in front of me as I address [the defense] and he's right there. I get to talk to him a little bit in the meetings. He hasn't missed a beat."

Mathieu is vaccinated, a source said. According to NFL rules, he can return to the Chiefs after two negative COVID-19 tests within a 24-hour period as long as he's also free of symptoms.