Milorad Cavic will forever be the man who got closer than any other to stopping Michael Phelps exceeding the Spitzean count of seven gold medals. 

One of the lethal qualities of the US-raised Serbian, in sporting terms, was an explosivity hard to match even in the world of sprinting. Back surgery in 2010, says Cavic, dimmed the spark that once threatened to burn Phelps.

As he emerged from the 100m butterfly at the Olympic tests event here in London, Cavic was asked how he was doing. "I've been better," he said with a smile and with a nod to a question about his back added: "Its never going to be the same. whoever has had the operation they've never been the same and its something that just goes along with the injury."

With Phelps one of only two men (in suits 100% and 50% shiny) to crack 50sec over 100m butterfly, Cavic named the drop: "I think what I lost the most was my explosivity." 

It was Cavic's ability to fire off the blocks and get to the first wall faster than anyone in the world could that prompted coach Bob Bowman to tell Phelps that he needed to be no more than 0.7sec behind the Serbian at the turn if he was to have a hope of beating him for the Olympic crown in 2008.

As things turned out, Phelps turned 0.62sec behind Cavic and took the gold just 0.01sec ahead of him, the closeness of the call prompting calls for Omega to "show us the proof" and explain how momentum, weight and angle on the wall (the way a swimmer finishes a race) are all critical to what splits gold from silver in the race pool. 

The flashback recalls: 

• Phelps: 24.04, 26.54, 50.58
• Cavic:  23.42, 27.17, 50.59

That 23.42 split matches the best Cavic has ever swum in a solo 50m race, for 14th best ever in textile back in 2007 and though he clearly could have been quicker since had he set his mind to the non-Olympic dash in peak form the speed of that split is otherworldly.

Thinking back to how it felt to leave the blocks before the surgeon's knife, could he explain the difference in feel then and now?

"I've had some really, really good therapy and I think I've been to the right people," said Cavic, coached by Andrea Di Nino. "The important thing is I don't feel pain but I feel limited: my upper body's good, my lower body's good but its about putting them together and making them work, about sending a signal for the legs to go. But somewhere in the middle it has to compute that message. I'm working on it."

The smile falling away a touch, he explained: "Most doctors a year before my operation told me that I'd never compete again, never be the same again. I thought that might be so, especially last year. It took me a full year to get back into it. I was just getting back into training around the world championships time but I wasn't ready for it. Since world championships been doing things differently. The other thing to keep in mind is that I'm not 20 anymore. It's not getting easier. I keep telling myself I'm getting too old for this."

He doesn't look it, his fitness level keen, his demeanour youthful. Even so, he looked ahead a few months and saw two ways to go:  "At the Olympics I will be one of the oldest dogs in the pool and it will be a matter of me walking away on my own terms with a medal or letting the other guys put me to sleep."

He was still in the sport "because I enjoy the sport and especially after such a surgery I realise that I like to do what I'm doing. The unfortunate thing is that you realise these things when its too late and its nearly all over. I think I'll be ready. I'm just lucky to be here. The aim for me would be to win a medal. I would be the first athlete ever to do that after back surgery."

Cavic's world may have changed but the showman survives intact, summer his season, super troupers, crowd and edge his roll calls to performance. 

"I think I shine in those moments. I love pressure, I do well with pressure," he says. "I heard this great quote a long time ago … 'when the devil smiles at a man all a man can do is smile back'. What that's about is just be in the moment, you're there, do or die, there will be no mercy on the other side, so for me it's just about attacking, attacking. I show that in my race. When it's all said and done I know there's nothing left in my tank and however it finishes I walk away knowing that I gave it my all."

After the duel with Michael Phelps in Beijing came shiny suit wars, Phelps refusing to join the 100% poly count as the X-Glide rattled the times on the clock another notch. Cavic suggested to Phelps that he could get an X-Glide for him before finals; Phelps said he'd let his swimming do the talking. And he did. Cavic too, both under 50sec. It was gladiatorial, with the greatest Olympian of all-time making his point: suit, no suit, fur coat, bring it on! Cavic loved it, even though he was portrayed as the Old Nick of Nuoto in the Roman arena.

Recalling the battle of words in Rome and the rub of the race, he said: "It's something that's necessary for the sport. The American media portrayed me as the evil villain with the black cape and you know I think that was kind of unfair but it's good for the sport and its kind of healthy if you really ask me I don't give a damn. I just needed a moustache [to be the ultimate villain for the US media].

"It's good for the sport and I wish there could be more of that going on. I'm not talking trash talk, I mean egging each other on. It can help our sport grow."

Phelps he said had "obviously done a lot for the sport but the sport would have really been at a different level if he'd wanted to [by engaging in more of the stuff of rivalry out of the water]. He's done everything he could, he's won everything and he's been the cross-bearer for the swimming world and everyone has got to be grateful for that but you can't help but wonder what it would have been like if there had been more of that going on. Rivalry is good as long as it doesn't get out of hand."

In London for the Olympic test event, Cavic described the Olympic pool as "fantastic … I couldn't imagine anything better" but reserved criticism for the physical therapy room. "It's not even close to what the Olympics will be: 1,000 swimmers and staff. Now, there's not even a couple of hundred people in that room and its really full. There's a lot of space in this pool, but it spread out. I think it could have been built a little better in that sense. 

"They knew the world was coming and in that sense, agains, when Olympics is past they are not going to need that extra space. Its economical and they will make it work. For me it'll be bad for everybody and we'll have a level playing field," he added with a smile. 

More on Cavic, his plans to become a member of the IOC Athletes' Commission in the near future and why Cuba has a squad heading for help at the Andrea Di Nino Project.