The world's number one player has grim words of warning for the world's most romantic rugby team. New Zealand's Dan Carter says unless Ian McGeechan's Lions come together quickly on the South Africa tour, they will be staring down the barrel of a second successive series whitewash.

"Nowhere in the world is it tougher to play rugby than South Africa. But on the other hand, those are the sort of challenges I like. It makes the rewards so much better when you win; there's no better feeling."

Carter, who returns to New Zealand this week after a seven-month sojourn with French side Perpignan, which was wrecked by a serious Achilles injury, said: "The Springboks will want to play well in this series, especially after all the hype and build-up. It'll be pretty tough for the Lions to win any Tests there, especially with two of the three at altitude. A lot of people are writing off the Lions already but I really hope they give some good performances and test themselves against the Boks. They have some good players but if they don't gel together as a team, they will find it extremely tough."

Carter warned the Lions that the same principles will apply in South Africa as in New Zealand four years ago when the Lions last toured. "The success rate of the Lions is not that great but the amount of history behind them and the way their fans get behind the team makes them special.

"I remember in 2004 when we played in Britain, there was already so much build-up in the media about the Lions tour the following year and that really got our motivation levels high. There is so much hype around it but that makes it hard for the Lions.

"The southern hemisphere teams play them so little we're lucky if we meet them once in our careers. You want to make the most of that once-in-a-lifetime chance. We prepared really well for that series and showed how much we wanted it."

He forecasts that the South Africans will be the same this month. "As soon as they won the World Cup, their focus was the Lions, not the Tri-Nations. And from the Lions' point of view, it is very tough to put a team together. That comes down to good management and coaching plus the players that are leaders standing up. In any successful team, you put your body on the line for the same goal, you fight for the same thing."

But it is the current strength of South African rugby that convinces Carter the Lions' task is immense. Coming just days after New Zealand outfit the Chiefs were slaughtered 61-17 by South Africa's Bulls in the Super 14 final in Pretoria, his words reveal a deep respect for the Springboks. "South Africa are in a great position. Winning the World Cup was huge but now they've also won the Super 14 in two of the last three years. Then the South African Sevens won their world series.

"There may seem to be a lot of political problems in their rugby but the teams and players are pulling through. They have some real athletes and the people love the game."

And the Springbok player the Lions should watch out for above all others? Bulls back-row player Pierre Spies is a player Carter calls "a monster".

"He is so fast and fit. His running off the back of the scrums and line-outs will represent a huge threat to the Lions." The New Zealander speaks from personal experience. "When you see him coming at you, there isn't much doubt in your mind about the challenge you're confronting" smiles Carter. "He is a great player and probably still has his best years ahead of him."