The Shrimpers have had a fantastic second half of the season and have lost just one of the last 16 games.
The Lancashire club are just four points behind seventh-place Chesterfield with a game in hand, but McIlroy thinks it will be a tough task to extend their season.
"I still think it's a big ask. We have got hard away games at Rotherham and Exeter," he told PA Sport. "But the way we have been going, we have a never-say-die-attitude so you never know.
"We have got to win the majority of our games. We're four points outside the play-offs so I think you have got to say we have got to win three of those games."