According to NFL Network's Tom Pelissero, the NFL and NFLPA believe Brown did not consistently wear his league-issued tracking device prior to the positive test. They are also looking into video of Brown hanging out with other Raiders offensive linemen while not wearing masks.
Raiders head coach Jon Gruden announced Wednesday that Brown had been placed on the reserve/COVID-19 list and that the rest of the team's starting offensive linemen had been sent home because of the fact that they were "around" Brown.
The 27-year-old Brown is in the midst of his second season with the Raiders after previously playing for the San Francisco 49ers and New England Patriots.
Brown, who is the Raiders' starting right tackle, was named to the Pro Bowl for the first time in his career last season.
In a season-opening win over the Carolina Panthers last month, Brown suffered a calf injury. He didn't return to action until last week when he started in Las Vegas' upset win over the Kansas City Chiefs.
Vegas is set to host the Tampa Bay Buccaneers on Sunday night football, but the team could be in trouble if any additional offensive linemen are unable to play.
Per ESPN's Paul Gutierrez, the offensive linemen who were sent home aside from Brown are eligible to return to the team facility Thursday as long as the COVID-19 tests they took Wednesday come back negative.
The tracking devices given to NFL players this season are called Proximity Recording Devices, and they are mandatory for players and coaches at the team facility, during practices and during travel.
They are key in determining the proximity between people, which aids in contact tracing after a player, coach or other personnel tests positive for COVID-19.
If Brown did not wear his Proximity Record Device, the Raiders could be subject to fines or other punishments by the NFL.
Assuming Brown is not able to play against the Bucs on Sunday night, the Raiders will likely either start veteran Sam Young at right tackle or move Denzelle Good from left guard to right tackle and slot rookie fourth-round pick John Simpson into the left guard spot.