Tom Pelissero of NFL Media reports Thielen tested positive but then tested negative for COVID-19. It is possible Thielen had a false positive.
More testing will determine whether Thielen is positive.
Vikings offensive guard Dru Samia also is on the COVID-19 list.
Vikings receivers coach Andrew Janocko missed Sunday’s loss against Dallas. The team included a line in its final injury report Friday that Janocko would sit out the game.
Thielen caught eight passes for 123 yards and two touchdowns in the loss to the Cowboys.
For the season, Thielen has 49 catches for 646 yards and 11 touchdowns.