McIlorum, 28, went off on a stretcher after a tackle on Broncos half-back Anthony Milford and went to hospital.
The Leeds-born England international has played 220 games for the Warriors.
"Micky could be out for six months," Wigan coach Shaun Wane told BBC Radio 5 live sports extra. "He's playing rugby league and these things happen."

The Travel Photographer of the Year Awards is staging the outdoor exhibition at Princes Dock Street.
The show is part of the second season of Hull's year as UK City of Culture.  Entitled Roots and Routes, it aims to celebrate Hull's role as a major port and its international connections.
The awards began in 2003 and accept entries from amateurs, semi-professionals and professionals.
Read more about this and other stories from Hull and East Yorkshire
See some of the winning entries
The photographs on display include a selection of winning entries from the 2016 competition.
Entrants from more than 120 countries entered the competition and photographers from 21 countries featured among the winners.
Martin Green, chief executive and director of Hull UK City of Culture 2017, said: "Our Roots and Routes season is all about celebrating Hull's global connections and its place in the wider world.
"This exhibition will give people in Hull the opportunity to see unique images of some of the planet's most famous and recognisable places along with exposing them to some far-flung and unfamiliar locations and sights."
The photographs will remain on show until 30 June.

Rhys Bennett, who was 12 at the time, was chased by the dog in a Leicestershire park, pulled to the ground and bitten on his face and body.
The dog handler said he had released the dog because he did not realise Rhys and his friends were children.
Leicestershire Police confirmed that an out-of-court settlement had been made.
However, the force has not apologised to Rhys or his family - despite this being the reason his mother began the compensation claim.
The attack happened on 13 October 2007, and the family's solicitor said the time it had taken to resolve the claim had added to the trauma.
Updates on this story and updates from Leicestershire
"This has been a truly traumatic experience for my client," said Dianne Collins of Nelsons Solicitors.
"The police dog handler concerned said that he did not recognise the people running away as children and if he had known he would not have released the dog.
"However, every other officer who was present that day did identify the 'runners' as children - and yet the dog handler still released the dog."
Rhys was playing with three friends in his local park in Sapcote when they tried to get into a derelict pavilion that had been boarded up.
Someone called the police and the children fled when officers arrived.
The dog handler released the dog and it chased the children, pulling a girl to the ground by the wrist, releasing her and reattaching to her side.
The dog then released the girl and attacked Rhys.
"It was terrifying. I couldn't move," said Rhys, who is now a 20-year-old engineering student.
"The dog's teeth bit into my lip and there was blood gushing everywhere. I was so scared.
"I was taken to hospital and it was all a bit of a blur."
As well as surgery to his face he needed counselling. He became too afraid to leave the house alone and could not even look at dogs for several years.
"Following the attack I was petrified of dogs and would cross over the road if one was walking towards me," he said.
"I'm less scared now, but I will never forget that day in 2007 and how scared I was. I was only 12."
The matter was set for a three-day trial this week but Leicestershire Police accepted the family's offer to settle for £10,000 shortly before the trial was due to start.
"No admission of liability was received nor was an apology - which was all that Mrs Bennett really wanted at the beginning of the claim," said Ms Collins.
"Rhys had never been in trouble with the police before and has never been in trouble with the police since."
Leicestershire Police said in a statement: "The training, deployment and management of police dogs within Leicestershire Police is constantly reviewed and developed in order to maintain the highest possible standards of professionalism."
Wigan hooker Michael McIlorum is facing a six-month lay-off after sustaining a suspected broken ankle in Saturday's World Club Series defeat by Brisbane.
[NEXT_CONCEPT]
A free showing of award-winning travel photographs has opened in Hull.
[NEXT_CONCEPT]
A man who needed facial reconstructive surgery after being attacked by a police dog as a child has been given £10,000 in compensation.