Conner was initially listed as questionable with a quad injury but was downgraded Monday.
He previously missed two games on the reserve/COVID-19 list but returned in the loss to the Buffalo Bills on Dec. 13. Conner has rushed for 100 yards or more three times this season, the last of his rookie contract.
In his return against the Bills, Conner had 10 carries for 18 yards, his lowest output since an injury-shortened season debut against the New York Giants where he had 9 yards on six carries. He has five touchdowns this season and is averaging 4.3 yards per carry.
Without Conner, the Steelers will turn to second-year back Benny Snell, who is averaging 3.3 yards per carry and has three touchdowns. Jaylen Samuels and Anthony McFarland will likely round out the group Monday night.