Minnesota Vikings wide receiver Ihmir Smith-Marsette (15) runs with the ball as Kansas City Chiefs safety Tyrann Mathieu (32) defends during the first half of an NFL football game Friday, Aug. 27, 2021, in Kansas City, Mo. (AP Photo/Charlie Riedel)
Minnesota Vikings wide receiver Ihmir Smith-Marsette (15) runs with the ball as Kansas City Chiefs safety Tyrann Mathieu (32) defends during the first half of an NFL football game Friday, Aug. 27, 2021, in Kansas City, Mo. (AP Photo/Charlie Riedel)

KANSAS CITY, Mo. (AP) — The Kansas City Chiefs remained without All-Pro safety Tyrann Mathieu after his positive test for COVID-19 as the two-time defending AFC champions began preparing Monday for their season opener against the Cleveland Browns.

Chiefs coach Andy Reid said that Mathieu, who was vaccinated against the virus, remained in the league's protocol, which means he had yet to return two negative tests taken 24 hours apart. That is the requirement for vaccinated players who are asymptomatic to return to their teams under the NFL rules released in July.

“We just have to wait that out and see where he's at,” Reid said. “I'll know more as we go on.”

The Chiefs are off Tuesday before returning for their first on-field work of game week Wednesday. They will also have a full practice Thursday before their typical quick Friday practice and Saturday walk-through, which means there is still a chance Mathieu will be able to join the Chiefs before the Browns visit Arrowhead Stadium on Sunday.

Mathieu starts in the base defense alongside Daniel Sorensen. And while the Chiefs have a pair of capable backups in Juan Thornhill and Armani Watts, Mathieu is the leader of a secondary that has become one of their defensive strengths.

He is coming off his second straight All-Pro season, and possibly the best of his career, picking off a career-high six passes with 62 tackles and three for loss. One of those interceptions came in a divisional playoff win over the Browns in January.

Asked where the Chiefs stood on vaccinations as a whole, Reid replied: “We're right at the top.”

“There are not many that are not vaccinated, I'll just put it that way,” Reid said. “I'm not sure what we're supposed to say and not say, but we're right at about 100 percent.”

The Chiefs already are missing middle linebacker Willie Gay Jr., who landed on injured reserve with a toe injury sustained in their preseason finale. The IR designation means Gay will miss at least the first three games of the season.

The Chiefs used their initial pick in April's draft to take Missouri linebacker Nick Bolton in the second round, and now he is in line for more playing time Sunday. The Chiefs will also turn to Ben Niemann, who has appeared in 45 games as a backup over the past three seasons, to fill in alongside veteran linebacker Anthony Hitchens.

“Nick had a good preseason,” Reid said. “He's worthy of stepping in there and playing. He'll get some play time for sure.”

The Chiefs are expecting a sellout crowd at Arrowhead Stadium on Sunday after the pandemic limited them to 22% of capacity, or about 16,000 fans, throughout last season.

That could be a big bonus for the Chiefs given they'll be playing a team that is expected to mount one of the biggest challenges to their AFC throne.

“Listen, I'm probably speaking for all of us that after watching this weekend with the college games, it was pretty amazing. I had goosebumps,” Reid said.

“You watch that and the people were into it. I almost felt like they were let out of a camp somewhere and, ‘Oh man, we have freedom again here,’ where we can go to these games. It was very exciting. I look forward to Arrowhead Stadium being just as exciting as its ever been and maybe a little more.”

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