Ireland's 57-15 hammering at the hands of Eddie Jones' England last Saturday was "a real set back" in their Rugby World Cup preparations, but former captains Brian O'Driscoll and Jamie Heaslip believe Joe Schmidt's side can still turn things around and come away from Japan with the Webb Ellis Cup.

Speaking to Kyodo News from Enniskerry, Ireland, the pair said there were realistically six sides that could win the World Cup, though as O'Driscoll pointed out, "you never know about France."

"Based on their performances in the last six months, England, New Zealand, South Africa, Australia and Wales, and Ireland based on the last 18 months," said O'Driscoll when asked who he thought could win the tournament, which kicks off in Tokyo on Sept. 20 and concludes in Yokohama on Nov. 2.

Ireland have yet to progress past the quarterfinals in a World Cup and O'Driscoll admitted the team -- whose final two warm-up games are against world No. 1 Wales on Aug. 31 and Sept. 7 -- were "running out of runway" in terms of preparation and building confidence.

"We need to get our confidence going and our mojo back if we are going to get beyond the pool stages and quarterfinals and potentially lift the trophy," said O'Driscoll, who played 133 times for his country and eight games for the British and Irish Lions.

(Brian O'Driscoll (L)and Jamie Heaslip)[Supplied photo]

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Ireland's draw, which sees them open their Pool A campaign on Sept. 21 against Scotland in Yokohama, followed by Japan a week later in Shizuoka before they take on Russia and Samoa, was "the best layout of a pool stage," O'Driscoll said.

"But if you lose one of those first two games, your back is immediately against the wall."

The 40-year-old former center, who is an ambassador for World Cup sponsor Land Rover, scored two tries when Ireland beat Japan 78-9 back in 2000, but he said the gap between the Tier 1 and Tier 2 teams had closed considerably since then.

"The defenses are tighter, there is more professionalism across the board and the intensity and fitness levels have levelled out."

And he was adamant that Ireland would not do what South Africa did four years ago and "take Japan lightly."

"You have to respect the host nation, particularly on the back of what happened four years ago. Ireland will not be taking liberties with Japan, knowing how much they will be up for the game."

Fellow Land Rover ambassador Heaslip, meanwhile, said the squad Schmidt has put together is the best Ireland have ever assembled, and while he was disappointed with last week's result -- particularly the speed at which the Irish played -- he was hopeful the team would rebound.

"The mistakes in defense are easy fixes," he said, adding that the more games they play the better they will become in reacting to the opposition.

Heaslip said he believed the team had the depth needed to win the tournament and that they would go into the tournament believing they are "going to win every game they wear the green jersey."

While O'Driscoll will be making his first trip to Japan, Heaslip has visited the country before to see one of his older brothers who used to live here.

And he said the travelling Irish fans were in for a treat.

"Japan is such an amazing country," said the 35-year-old former No. 8, who represented his country 95 times and played five tests for the Lions.

"In some ways it is similar to other places you might visit but in other ways it is so, so different, culturally and traditionally. I think it is going to be a real good experience. It's so easy to travel around and has so much variety within its borders as well. People are in for a real mix of really old and really new."

"It really is a once in a lifetime opportunity for people to get over there."

O'Driscoll, meanwhile, was hopeful the Japanese fans would experience the best of rugby.

"The values of the game both on and off the field are quite similar. It's about respect, camaraderie and enjoying one another's company and there's a real friendliness that comes with Rugby World Cup," he said.

"I hope Japan gets to experience the best of rugby in that regard. It is a huge opportunity for the game to take a step forward in its progression and hopefully we get a Rugby World Cup to savor."