Tim Henman has urged Wimbledon sensation Marcus Willis to believe he can beat Roger Federer when the world number 772 tackles the "best player that's ever played the game".
The former British number one says it would be a far bigger upset for Willis to sink the seven-time champion on Wednesday than it was for football minnows Iceland to take down England in their Euro 2016 clash.
But Henman says 25-year-old Willis must enjoy his moment in the spotlight, and be positive against his vaunted opponent.
Towards the end of his own playing days, Henman knew the teenage Willis as they shared a club, and identified him as a talent whose lifestyle and attitude were not that of a potential top player.
Willis admits he was majorly overweight barely 18 months ago, and in danger of wasting his ability.
And Henman told Press Association Sport: " I've known him for a long time because when I moved out of London while I was still playing, I was based at Bisham Abbey, and that's where he used to be based.
"He was always a kid with a lot of character, but if anything lacked the commitment.
"He wasn't in good enough shape. Now it's one of those dream stories, and that's what makes Wimbledon special."
Henman won six of the first seven matches he played against a young Federer, before losing the next six for a career 7-6 head-to-head record in favour of the Swiss.
He is a close friend to Federer but pointed to the injuries and illness that have affected the 34-year-old this year, possibly offering Willis a glimmer of hope.
"In sport and especially in a two-horse race you've got to go on the court with belief, and for Marcus to have that opportunity he's got to go out there with a game plan and good luck to him," Henman said.
"It'll be amazing for him, his family and supporters, and a fun match to watch."
After winning six preliminary matches to qualify for Wimbledon, Willis thrashed Ricardas Berankis, Lithuania's world number 54, in the opening round.
Henman was impressed but suspected if Willis was going to make it on the big stage anywhere, it would be at Wimbledon.
"In tennis you've got to have three elements: you have to have the game, you have to have the physicality and you have to have the mentality," Henman said.
"He's struggled in a lot of those areas, but on grass, given the conditions and how comfortable he is, because he's got a very good leftie serve, he can make life difficult."
But as for clues on how to beat Federer at Wimbledon, which Henman achieved in 2001, when the future champion was just 19 years old, Henman was struggling.
"With difficulty," Henman said, speaking on behalf of HSBC during activity on their Court 20 area alongside the famous Wimbledon queue.
"You certainly have got to play some great tennis.
"Federer has had the most difficult year of his professional life, to need knee surgery - the first of his career - and he's had illness and hasn't had a lot of match play.
"The advice for Marcus would be to take your time. It's very easy in a big match with the lack of experience for it to go very quickly. But he should soak up the atmosphere. He's had an unbelievable run and should give it his best shot."
And if Englishman Willis can deliver sporting success for a nation left dumbfounded by the Three Lions' loss to Iceland, all the better.
Henman says Willis knocking out Federer would surpass even Iceland's achievement though.
"I think it would. I think that puts it in a timely context," Henman said. "I think it would be a much bigger shock if Willis beats Federer."
:: Tim Henman is an HSBC ambassador. HSBC is the Official Banking Partner of The Championships and is committed to supporting tennis from the back garden to Centre Court. Follow @HSBC_Sport