The 23-year-old Pro Bowler suffered the injuries on the same play during the second quarter of Pittsburgh's 21-7 loss to the Cleveland Browns in Week 11. He did not return to the game, though ESPN's Jeremy Fowler reported three days later that the "knee injury is not serious for the long term."
When healthy this season, the 2017 second-round pick leads Steelers receivers with 524 yards and three touchdowns on 38 catches. Since entering the NFL, the USC product has tallied 2,867 yards and 17 touchdowns across 40 games.
Smith-Schuster doesn't have an extensive injury history. He played all 16 games for Pittsburgh in 2018 while only missing two outings as a rookie in 2017.
If the injuries keep Smith-Schuster sidelined, rookie third-round receiver Diontae Johnson will likely see a bigger role in the offense. The Steelers can also lean on tight end Vance McDonald and receiver James Washington.
Pittsburgh (5-5) could really use a win over the winless Bengals (0-10) to help bolster its playoff hopes in the crowded AFC. But it will need to do so without Smith-Schuster and running back James Conner, who's out with a shoulder injury.