The 29-year-old conceded the second-half penalty that Reims converted and was then sent off for making obscene remarks to the referee.
"What's unforgivable is to go and compromise the balance of the team and get sent off due to a lack of self-control, because once the penalty's been given, it's been given," Aulas told L'Equipe.
"For an experienced player, it's a 'sackable offence' which must not be pardoned. Milan must think about the consequences for the squad and the club."
Lyon are currently fourth in Ligue 1 with 53 points from 31 matches.