Johnson, who leads the team with 1,110 receiving yards and eight touchdown catches on 100 receptions, is a key member of the offense for the Steelers' regular-season finale against the Baltimore Ravens.
Under new return-to-play protocols adopted in December, NFL players who are vaccinated and asymptomatic can return to practice and games based on a measure of their viral load, known as the cycle threshold, or CT. That testing can begin as soon as one day after the initial positive.
Johnson had two touchdowns and 105 receiving yards earlier this season against the Ravens, who have the league's worst pass defense.
Defensive coordinator Keith Butler is also in protocols, though coach Mike Tomlin didn't rule him out for the game Sunday. Tomlin said defensive playcalling duties would be determined "at the 11th hour."