All Blacks great Keven Mealamu has been ruled out of tomorrow's Fight for Life main event after a routine medical check-up discovered a medical heart issue.

An ECG test yesterday confirmed he has an irregular heartbeat as part of a heart condition called Atrial Fibrillation. AF can present without symptoms and patients do not know they have the condition until it comes up in a routine check-up.

Mealamu had been "feeling a million dollars" ahead of the clash with league great Wairangi Koopu but after a routine check-up with his former Blues rugby doctor Stephen Kara yesterday, it was revealed he is unfit to fight.

"Keven feels numb and is so apologetic, typical of the man who has given so much but is thinking of others. That attitude to never want to let anyone down is what makes him special," says trainer and mentor Monty Betham.

Mealamu had worked tirelessly to be more than ready as one half of the main event but is left with no choice but to pull out of tomorrow's event. There are ways to manage or get the heart back to a normal rhythm but the priority is his health.

The risk he could face if he boxed is that if his heart rate goes too high, it could lead to chest pain, shortness of breath and could result in heart failure. There is also an increased risk of a stroke or heart attack from the clots that can form.

"We now must ensure Keven is safe. Whilst we must not allow Keven to fight, it is expected that he will make a full recovery," Betham said.

The event is going ahead as planned with Carlos Spencer and Paul Whatuira elevated to main event.

"This is worthy of being a professional fight, with both guys bringing in freak athleticism and boxing experience," says Betham.