England begin their World Cup defence today with head coach Brian Ashton insisting his players ''can pose all sorts of problems'' for rival teams.

While Ashton's men should encounter few anxious moments against a lightweight United States outfit in Lens, serious business is barely a week away with the imposing form of South Africa looming large.

Stricken fly-half Jonny Wilkinson remains a major doubt for that Stade de France showdown after suffering an ankle ligament sprain during training this week.

The England camp are saying little about his condition until next Tuesday, and Wilkinson's enforced absence must be put out of their minds for a Pool A encounter they will be expected to win by at least 50 points.

Medical opinion from outside the England squad suggests Wilkinson could be sidelined for six weeks, ending any chance of him playing in the World Cup.

Ashton said: ''Jonny is being assessed again next Tuesday. I have seen the speculation, and I have made no contact with anyone about being on stand-by.

''There is a possibility he will be fit for South Africa. We will need to know the situation on Tuesday, because that is three days before the South Africa game.''

Today's game is the 41st on England's schedule since they were crowned world champions in Sydney almost four years ago.

But just 16 victories - a 40 per cent success rate - underlines the extent of their demise, which is confirmed through an official International Rugby Board world ranking of seventh.

They also arrive in the tournament after failing to score a try during home and away warm-up games against France, raising acute concern about England's inability to break down world rugby's best defences.

Ashton added: ''We are looking for a little more accuracy than we have shown recently, and if we can also get through the game without injuries then we will be pretty satisfied.

''We have analysed the opposition because it would be disrespectful not to, but we've focused a great amount of our attention on our own game. We are not in a position to do anything else.

''If you start thinking about racking up a specific number of points you put yourself in dangerous territory. The important thing is to get the key processes right.

''I have full confidence the players will rise to the occasion.

''We can pose all sorts of problems for all sorts of teams in this World Cup if we play to our potential.

''You can't play the World Cup down. It is the biggest tournament in world rugby, and people feel incredibly privileged to be involved.''

England's World Cup build-up effectively began almost 11 weeks ago through team-building exercises with the Royal Marines and then an intensive training camp in Portugal.

More fine-tuning took place on a regular basis at the University of Bath, but a sense of urgency among the players is almost tangible as their tournament kick-off approaches.

Skipper Phil Vickery said: ''South Africa are looming large, and if we do well in that game then suddenly we will be being talked about.

''There is a lot of belief among the players, but we just want to get on with it now. Things have dragged on and on.

''We should win this game against the States, and win it convincingly, but they have a lot of good, solid players and they will be up for the game.

''In terms of physical conditioning, I think the gaps between sides have closed.

''You have to respect these guys. They are a proud nation playing the defending champions in their opening game of the World Cup.

''They will be physically and emotionally charged.''

With Wilkinson out, Bath's Olly Barkley takes on the fly-half role, while Andy Farrell provides bench cover, both for the midfield area and goalkicking.

England should encounter few problems winning a plentiful supply of possession, but the big question will be what they do with it.

Given the back three of Mark Cueto, Josh Lewsey and Jason Robinson boast 61 Test tries, it would be a criminal waste of ball if that impressive tally is not increased considerably by tonight.

England will encounter an American pack fine-tuned by one of New Zealand's top technical coaches.

The United States have placed a huge emphasis on forward power under the guidance of All Blacks forwards expert Mike Cron. USA scrum coach Bill LeClerc said: ''We were fortunate to have worked with Mike and we have implemented a lot of his techniques."