England backs coach Andy Farrell fears Wales will use the loss of Leigh Halfpenny and Rhys Webb to fuel their quest to emerge from the toughest group in Rugby World Cup history.

British and Irish Lions points machine Halfpenny and scrum-half Webb, their in-form player over the last year, have been ruled out of the tournament through injuries sustained against Italy on Saturday.

It is a disastrous setback for Warren Gatland's men, who must now lock horns with heavyweight Pool A foes England, Australia and Fiji without two of their most established stars.

But Farrell, who worked with Gatland and Halfpenny on the 2013 Lions tour to Australia, believes Wales will circle the wagons in response to their absence with the Six Nations rivals scheduled to collide at Twickenham on Sep. 26.

"Wales are not down. Warren will probably use the injuries to create bit of a 'backs against the wall' mentality. That will strengthen them and galvanise them even more," Farrell said.

"Some people would say that it weakens them a little bit but we don't see that. The strengthening of the team and the team coming together is more important than the loss of any individuals."

Halfpenny has been ruled out with knee ligament damage and Gatland's decision to play him on Saturday has been criticised by former Wales wing Shane Williams, who said the full-back should have been wrapped in "cotton wool" and noted the strapping to his leg before the match.

Farrell absolves Gatland of blame and notes the good fortune enjoyed by England so far on the injury front. Centre Manu Tuilagi and hooker Dylan Hartley are missing but their absence is for disciplinary reasons.

"Players need game time. We have been training for 10 and a half weeks and the reason you train is so that you can play well," Farrell said. "That's where it matters - out on the battlefield in the international arena. There's no substitute for actually putting yourself in those situations.

"You have to have these warm-up games otherwise you become completely undone. "Injuries are always going to be part of the game and we feel very fortunate that we have come through unscathed.

"Leigh himself would have wanted to play. He would be a big loss to any side, he's a great player and will be sadly missed in the competition.

"He's as good a kicker as there is in world rugby, he's a phenomenal goal kicker."

The Lions tour to Australia was also where Farrell worked with Mike Phillips, the veteran scrum-half who has been called up to replace Webb.

"It's not a bad replacement, an angry Mike Phillips. After missing out in the first place he will want to prove a point," Farrell said.