Benali, who played nearly 400 games for the club in an illustrious career, is attempting to raise £1 million for Cancer Research UK by running between all 20 top-flight grounds.
The challenge has never been done before and will see the 45-year-old cover 40 to 50 miles a day for 21 consecutive days.
Benali’s Big Run, which will start at Newcastle’s St James’ Stadium on August 24, has been a challenge that the former full back has been eager to undertake for some time.
The gargantuan task will see Benali meet up and run with friends and former pros, including Saints legend Matt Le Tissier, ex-Dell players Neil Maddison and Tommy Widdrington en route.
He also wants to rope in Alan Shearer when he’s in Newcastle, who played for Saints between 1987 and 1992, scoring 43 goals in more than 150 appearances, and wants anyone, especially Saints fans, to join him on his travels.
“I’d say this is the craziest thing I’ve done, but some people might doubt that if they saw my playing career,” he laughed.
“It’s pretty extreme. I’m no fool to think it will be straightforward.
“I’m sure there will be some tough times ahead for me but in a strange way I’m looking forward to that as well, to see what my body can cope with, and what I can overcome.”
Le Tissier, the goal-scoring Saints legend who scored 209 goals for Saints, said about his friend’s challenge: “It’s not the sort of thing I’d like to be doing.
“I’m not the kind of person that looked forward to pre-season training, so this kind of run doesn’t come into my thoughts at all.
“Fair play to him, it’s a heck of a challenge and knowing his mentality, if there’s a 45-year-old man that can do it – it would be him.
“It baffles me how someone can even think about doing that amount of running to be honest.
“I will be joining him for two or three of the ten miles legs that he does.”
Benali will be joined by a support team and will run alonside his son Luke and daughter Kenzie.
The event, which has been sponsored by telecommunications firm 4com, has taken a lot of preparation.
“It’s an unbelievable challenge and the organisation is the same,” said challenge coordinator Karen Collier.
“All the preparation has started. Fran is sticking to a training plan, he is having ice baths and rubdowns, and it’s just about continuing what he’s been doing now.
“Some of the organising has been done at short notice and it’s been a very busy time but it’s been great fun so far.”
People can sponsor Benali by texting BIGR55 £3 to 70070 or donate at benalisbigrun.com.