The Steelers placed Johnson and running back Anthony McFarland on injured reserve on Monday, hours before Pittsburgh (0-1) hosted the Cleveland Browns (1-0).
Johnson tweaked his right hamstring while being tackled at the end of a 26-yard gain in the third quarter of a 30-7 loss to San Francisco in the season opener.
Pittsburgh coach Mike Tomlin had already ruled Johnson out against Cleveland. The move to injured reserve means he'll miss at least four games.
Johnson is Pittsburgh's leading receiver over the past four seasons, averaging 85 receptions a season since being taken in the third round of the 2019 draft. He was a Pro Bowler in 2021.
McFarland, who serves as the Steelers' primary kickoff returner, is dealing with a knee injury.
Pittsburgh promoted running back Qadree Ollison to the 53-man roster. The move is a homecoming for Ollison, who starred at the University of Pittsburgh from 2015-18 before bouncing around the NFL. Ollison's previous stops include Atlanta, Dallas and Jacksonville.
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