Bob Willis concedes Kevin Pietersen's series-ending Achilles injury will be a great loss for England.

Pietersen - suffering from the nagging injury during the first two Tests of the Ashes series - has been forced to undergo surgery on his Achilles tendon, and will require at least six weeks of rehabilitation.

His absence leaves England with a notable selection headache, as Andrew Strauss' men will be forced to play without their most consistent batsman.

"It's very bad news for England," Willis told Sky Sports News.

"He's been hampered by his injury in the first two games and quite clearly badly hampered at Lord's. It looked as though something was seriously wrong, and so it has proved."

"He never admits that anything is wrong with his game, but by the end of the match he had to concede that things weren't quite right."

"He looked mentally a little bit disengaged from it all, almost knowing that this inevitable decision was going to have to be made."

Despite the setback, England's top order enjoyed some success against the Australian attack at Lords, a fact not lost on Willis.

"Apart from Bopara all the batsmen have been getting runs, so I don't think there will be a panic in the camp."

As England also sweat over the fitness of Andrew Flintoff, their priority now is to decide who will assume Pietersen's spot in the batting order.

With Ian Bell performing admirably for Warwickshire in the County Championship, the former England fast bowler admits he is the front-runner to fill the vacancy.

However, Willis believes England may have to shuffle their line-up to accommodate the Edgbaston-based player.

Bell is no newcomer to the Ashes - having participated in the past two series - but his temperament has often been called into question. And with Ravi Bopara struggling, he argues that moving Paul Collingwood into the number three spot could offer the ideal solution.

"When Paul's batting well I think he's well suited to batting at number because he's a more defensive player who likes to play himself in before playing any expansive shots."

"The game is 80 percent played in the mind and clearly Collingwood has showed over the years - not just in Cardiff - that he is mentally very strong indeed. Just the sort of character you need to take on a fresh challenge such as batting at number three."