England's middle order has struggled in Pietersen's absence
England batsman Kevin Pietersen has suffered a setback in his recovery from Achilles tendon surgery because of an infection in the scar tissue.
The England and Wales Cricket Board confirmed the 29-year-old is back in hospital for further treatment but is due to be released on Wednesday.
Pietersen was operated on after his movement became increasingly restricted through the first two Ashes Tests.
The surgery already meant he would miss the final three matches of the series.
The injury first surfaced on England's tour of West Indies in March.
However, Pietersen's recovery was slowed when he strained the tendon again while playing for the Bangalore Royal Challengers in the Indian Premier League in April.
The Hampshire right-hander then missed the one-day series when West Indies made a return visit in May.
Despite clearly struggling at the crease, he averaged 38.25 from four innings at Cardiff and Lord's in the current Ashes series.
The ECB originally estimated Pietersen would be absent for six weeks and he has been named in England's initial 30-man squad for the ICC Champions Trophy, which begins in South Africa on 22 September.