Dichio was given his marching orders for an off-the-ball altercation with Forest's Wes Morgan in the 63rd minute - just seconds before he was about to be substituted - and will now be suspended for three games.
With only four games left, that would mean the former Sunderland and Sampdoria hitman will miss the game against Manchester United at the Millennium Stadium if Millwall fail to make the play-offs.
With captain Kevin Muscat already ruled out through injury and Nick Chadwick set to return to Everton once his loan spell is completed three days before the final, this is another blow manager Dennis Wise could well do without.