CLEVELAND — Case Keenum’s expected start for the Browns took an unexpected turn.

Cleveland’s veteran backup quarterback tested positive Thursday for COVID-19, possibly leaving the team without its top two quarterbacks for Saturday’s game against the Las Vegas Raiders, a person familiar with the situation told The Associated Press.

Keenum was slotted to make his second start this season for Baker Mayfield, who tested positive Wednesday as the virus continues to wreak havoc with the Browns and several other NFL teams.

Third-string quarterback Nick Mullens is now positioned to start against the Raiders, but nothing is set. Mullens was signed to Cleveland’s practice squad on Sept. 1 and activated from the practice squad Thursday as a COVID-19 replacement.

Keenum’s positive result came after he practiced on Thursday. The team is also placing safety Ronnie Harrison, linebackers Grant Delpit and Jacob Phillips and cornerback A.J. Green on its swollen COVID-19 list, said the person who spoke on condition of anonymity because the situation remains fluid.

The roster moves aren’t officially done, but once they are, the Browns will have 21 players on the COVID list. And coach Kevin Stefanski is also currently sidelined after his second positive test in two seasons.

Despite Cleveland’s widespread outbreak, a league spokesman said there has been “no change” for Saturday’s game as the Browns (7-6) and Raiders (6-7) try to improve their chances of making the playoffs.