“A lot of times after a match you wake up in the middle of the night and you’re like ‘Oiyaya!’,” says Jacques Burger, smiling, as he explains the bruising consequences of being one of the toughest and most committed tacklers in world rugby. “You can’t get out of bed. Everything hurts. It feels like you have been in a car accident. You tell yourself you won’t be able to train the following day. Yet you always do. Rugby is a brutal game but I wouldn’t change it for the world. I love it.”

And Burger, the captain of Namibia, expects to enter a new world of pain after his side have played the world champions, New Zealand, at the Olympic stadium on Thursday night. The prospect does not make him flinch. In fact he welcomes it. “One good thing about playing the All Blacks is that I’ll get more opportunities to tackle,” he says. “I am relishing the challenge.”

The bookmakers are predicting a massacre, the biggest mismatch of the entire Rugby World Cup. But when told that his side are 77-point underdogs, Burger raises an eyebrow. “It will be closer than that,” he says. “It’s not about the scoreline for us, rather those small victories in the match, but we will surprise a lot of people, I promise you. After the game people will be saying, ‘Geez, where did this guy come from?’ A lot of guys will get scooped up by bigger clubs.”

Rugby World Cup preview No15: Namibia Read more

Burger understands why people are writing Namibia off. They are the lowest ranked team in the tournament and their 23-man squad for Thursday night’s game contains eight amateurs, including four students. But he has seen the hard work his players have put in during training and says that amateur players such as the flanker Tinus du Plessis, a foreign exchange broker, and the full-back Johan Tromp, a salesman at a cycling shop, will not be overawed.

“These guys are incredible,” says Burger. “They wake up at four, five in the morning, start training at six, have to go to work all day and come back in the evening, six to half-seven, which is so challenging. That said, we have not played a match in four weeks so it will be hard against the All Blacks, especially the first 40 minutes. The game will be very quick so the lungs will burn a little bit.

“It will also be interesting to see what our mental state is when we rock up to the match. But I think the guys will be really up for it. Their skill level is of a really good standard, they are physical and they have been working so hard. They are ready for the battle.”

And so is Burger himself. During the past six years he has undergone nine major operations, while his boxer’s nose has been repaired “four or five times”. Yet his commitment to hurling his 32-year-old body into opponents remains undiminished. After inspiring Saracens to victory against Northampton in May, the Guardian hailed him as a “Demolition Man”, who was “oblivious to pain”, and he regularly gets called the toughest man in rugby. Burger shrugs when asked about the sobriquet. “Every time I get back from my injuries, people ask whether I will change the way I play,” he says. “But I don’t know any other way.”

So what happens when some 6ft 4in, 17 stone player – a Sonny Bill Williams, say – is charging towards him? What goes through his mind?

“It’s one thing to try to smash people left, right and centre but there is a lot of skill that comes into it too,” he says. “You have to know when to come off the line. When to go low. When to go for the ball to prevent the offload. All those decisions you make in an instant. The more you play, it just kind of happens.

“But while a coach can tell you where you should be positioned, at the end of the day you have to have the mentality that you want to hit somebody. If you want to make a big hit, there has to be no fear. And I don’t have fear on a rugby pitch.”

Burger nods when it is suggested to him that, despite being 6ft 2in and 16 stone, he is not especially big for a back-row forward. “Even the backs are bigger than me these days,” he says. “They are all so massive. The game is getting bigger and bigger. But, if a guy runs at me – whatever his size – I will try to hit him as hard as I can. That’s something you have to want in your soul. It’s something you can’t teach.”

Perhaps not. But Namibia’s Welsh coach, Phil Davies, says that Burger’s commitment and drive can inspire his squad in training every day. “He’s a great leader,” he says. “I’ve coached people like Sam Warburton, Gethin Jenkins and Stuart Lancaster and he’s right up there with the best. His relentlessness and dynamism in training is amazing. He’s in fifth gear all the time. There’s a huge spirit within the group and a lot of it is down to Jacques.”

This will be Burger’s last World Cup, having announced last week that he intends to retire next May. He plans to stay in the game as a defensive coach, possibly in France or Italy or maybe in an emerging nation such as Canada or the United States for a few years, before heading back to his 14,000-acre farm in Namibia. But right now Burger has more pressing business to tend to. And this most rugged of men admits he is not beyond dreaming about the impossible.

“I’ve actually thought about us beating the All Blacks,” he says. “But let’s say a couple of things happened throughout the match, and we scored a couple of great tries,” he pauses. “But realistically they are stronger and faster than us and we know that.”

His tone changes. He could be in the dressing room now, directly addressing his men. “So we need to work harder than them. We need to chase harder. We need to match them in the work that people sometimes don’t see, such as getting off the ground quickly to make the next tackle. We need to be brave. And we need to put in a very brave performance.”