Reckon you could swim almost four kilometres? Or cycle 180 kilometres? Or run a marathon?

Now imagine doing those sequentially, pauses prohibited. It’s what they call an Ironman triathlon. It’s what former NFL wide receiver Hines Ward called “torture for the insane.”

Now, if you haven’t been rendered faint just thinking about it, imagine doing seven Ironman triathlons over seven successive days. And at the age of 50.

That is the superhuman feat Franny Benali, the former Southampton defender, embarked upon this Monday morning in an attempt to raise £1 million – and some – for Cancer Research UK. It is the human fundraising factory’s third ultra-endurance challenge for the charity, but IronFran is emphatically his most excruciating.

“I guess I might be crazy,” Benali told FIFA.com, chuckling. “There’s been once or twice during training that I’ve asked myself that question.

“I remember how tough it was to play against Alan Shearer, [Jurgen] Klinsmann, [Eric] Cantona, Ian Wright, and you’d come off feeling it, but I don’t ever remember feeling exhausted during my football career. This is entirely different.

“The plan is to be in the water for 6 o’clock each day. The estimate, going on my training, is that it will take 16-18 hours, so I should be finishing between 10 o’clock and midnight. Then there’s recovery [exercises]. That’s going to leave very little time for sleep, and I love my sleep! It’s probably going to be a 5 o’clock wake-up call.”

The idea for hell was concocted in heaven.

“Me and my wife Karen were on lying on sunbeds on a cruise – bliss – last year when we came up with the idea. It had to be something bigger, something that would catch people’s imaginations.

“Adding a third discipline seemed natural, but I couldn’t really swim. Fortunately, the lady who taught my children, Luke and Kenzie, to swim when they were kids has been coaching me, so that’s a nice connection.”

Nice thoughts are certain to be substituted by torturous ones over the next seven days as Benali is relentlessly body-slammed to breaking point. What will keep him from surrender?

“The target is to raise £1 million for Cancer Research UK, and to hopefully smash through it and raise as much as we can,” said Benali. “I guess there’s an element in my mind that if I was to give up, the donations could be affected.

“It’s such a tremendous cause. It will help improve treatments for cancer and recovery from it. It will help so many people.

“And the support I’ve received has been absolutely mind-blowing. If I was to quit, it would feel as though I was letting people down.”

A portion of that support has come from planet football, with Mick Channon, Ray Clemence, Robbie Fowler, Matt Le Tissier, Michael Owen, Alan Shearer, Jeff Stelling and Phil Thompson putting their considerable vocal muscle behind IronFran.

“The support I’ve received from the football world has been sensational,” Benali said. “It’s really helped drum up interest for the cause.”

'The Beautiful Game' has helped Benali prepare for the ugliest week of his life on multiple levels.

“I've had a stubbornness, a drive to never give in since my football days," said the TV pundit. "I’ve battled through injuries. I once broke my arm in a game against Leicester away and played on for the remaining 30 minutes. I’ve always been able to block out pain.

“Maybe I was a little bit ahead of my time. There were a lot of cultures back in the day… I’ve never been drunk in my life, I’ve never smoked, I’ve always tried to lead a healthy lifestyle so I could train well. I was always conscious about how I prepared for games.

“And that’s continued in this challenge. I enjoy my takeaways, treats but there hasn’t had to be too much of a lifestyle change.”

Benali made 389 appearances during 16 years at Southampton. His career capstone was its solitary goal: a splendid header against Leicester.

“I celebrated that goal wildly,” Benali remembered. “It had been a long time in coming – well over 200 games. It was a great feeling.

“But if I cross the finish line in this challenge, I’m sure it will feel even better because I know how much the money will benefit so many lives.

“I’ve promised my family this will be the last one. I’m not getting any younger. I have to think about my health and well-being, and the toll it takes on my body.”

A 50-year-old putting his body through 27 kilometres swimming, 300 running and 1,260 cycling over seven days seems exclusive to a comic book. Iron Man is evidently not alone in having superhuman durability as a superpower. So, too, does his real-life alter-ego Iron Fran.

Francis Benali's Ironman endgame makes it seriously hard to reject him being every bit as fictional as Tony Stark…