Austin’s stamp on Forest’s Ryan Yates in the 43rd minute of the game was missed by officials at the time but picked up on camera.
The Rs forward was subsequently charged and, though he denied the incident had constituted violent conduct, was found guilty by an independent regulatory commission, the FA announced on Friday.
Austin has been in terrific form for Mark Warburton’s side since returning to the club on loan from West Brom in January.
The Rs were facing a potential relegation scrap at that point but have now pulled well clear of the drop, currently sat in 12th, with Austin scoring six times in 17 appearances.
The suspension means the 31-year-old will miss this Saturday’s home game against Sheffield Wednesday, as well as away trip to Rotherham and Middlesbrough.
He should be available to return for the away visit to promotion-chasing Swansea on April 20.