McIlorum was given the suspension, along with a £300 fine, following his 16th-minute dismissal in last Friday's 26-18 derby defeat by St Helens for a high and late tackle on Saints prop Anthony Laffranchi.
Wigan contested the severity of the suspension, arguing that he had already effectively sat out one match because of his early dismissal, but the appeal was rejected at a hearing in Leeds on Wednesday evening.
McIlorum will begin his ban when the Warriors take on Catalan Dragons in the first qualifying play-off at the DW Stadium on Friday, when a victory would take them straight through to the semi-finals and to within 80 minutes of the Grand Final.
McIlorum's only chance of playing in the final would come if Wigan lose to the Dragons - because it would mean an extra game the following weekend against one of the winners of this weekend's elimination play-offs - and go on to win their next two ties.
Coach Shaun Wane has the option of bringing in inexperienced hooker Logan Tomkins, younger brother of full-back Sam, but has not named him in his 19-man squad for Friday's game.
Instead Wane is likely to use half-backs Matty Smith and Thomas Leuluai in the hooking role, of which both have past experience.
Former Hull prop Epalahame Lauaki, who has missed Wigan's last two matches of the regular season, has been included in Wane's initial squad.
The Catalans are still without former Bradford and St Helens stand-off Leon Pryce, who is still recovering from a knee injury, but have prop Lopini Paea returning from injury.