The suspension, announced Tuesday, stems from Mendenhall's absence from Heinz Field on Sunday after he was told by the team he would not dress, The Pittsburgh Post-Gazette reported.
The Steelers suffered a disappointing 34-24 loss to the Chargers.
Mendenhall has been inactive for the past two games since fumbling twice in four carries in Cleveland. He is an unrestricted free agent after this season.
Pittsburgh has signed Baron Batch from the practice squad.
Mendenhall has also been slowed this season by injuries. He tore the ACL in his right knee in Week 17 last season and didn't make his return until Oct. 4 this year. His return didn't last long though, straining his right Achilles four days later.
The Steelers (7-6) head to Dallas to take on the Cowboys this week and hold the sixth and final playoff spot in the AFC.
Information from The Associated Press was used in this report.