London, July 23 : The England team's middle order has become a bit vulnerable and pressure has increased on other players to perform after star batsman Kevin Pietersen was ruled out of the Ashes series due to injury.

Pietersen, who had been troubled by the injury for the past six months, had surgery on Wednesday after seeing a specialist from Sweden and will be out of cricket for at least six weeks.

His place in the squad will almost certainly be taken by Ian Bell, with Owais Shah, Joe Denly or Stephen Moore being included as cover in case of any last-minute injury, The Telegraph reports.

"Following a consultation, involving scans and testing, with the world''s leading Achilles specialist, Kevin Pietersen today underwent surgery on his right Achilles tendon," Nick Peirce, the England and Wales Cricket Board chief medical officer, said.

Pietersen's absence certainly makes England's middle order look a bit more vulnerable, though with both sides having to work hard for their wickets.

The ECB has not yet revealed the cause of Pietersen's Achilles problem, but it was aware the injury had been troubling him during the West Indies tour.

Medical opinion has subsequently said that Flintoff's injury could have happened at any time, but England's management knew Pietersen was struggling with his Achilles when they granted the No Objection Certificates. (ANI)