Kevin Pietersen's bid to be ready for the start of the Ashes was cast into further doubt last night after he was ruled out of the Champions Trophy with an increasingly worrying knee injury.

England's talisman will not return to action until mid-June after an MRI scan revealed only "some improvement" to bruising in the bone of the right knee he injured during the tour of New Zealand.

The 32-year-old will therefore have less than a month to prepare for the Ashes opener on July 10, on the proviso this latest assessment proves correct.

Already Pietersen's recovery has become protracted, with the initial "six to eight week" diagnosis being pushed back to now rule him out of New Zealand's return tour as well as the Champions Trophy from June 6-23.

"Kevin Pietersen has been ruled out of the ICC Champions Trophy following a repeat MRI scan on his right knee," an ECB statement read.

"The scan has shown some improvement in the bruising to the bone that occurred in the build up to the Test series against New Zealand in February.

"However Pietersen will not have recovered sufficiently in time for the NatWest one-day series against New Zealand beginning May 31 and the ICC Champions Trophy which follows.

"Pietersen will now start a graduated rehabilitation program with a view to resuming full training by the middle of June.

"That date would allow Pietersen the opportunity for a maximum of two LV= County Championship games with his county side Surrey before the five-Test series against Australia.

England's focus will now, however, be on ensuring he is fit enough to make his return at that time following this latest setback.

Pietersen flew home from the tour of New Zealand on March 24, on the eve of the third Test, after revealing could no longer play through the pain of an injury sustained in the warm-up game in Queenstown.

Scans on his return to England initially offered an optimistic diagnosis with surgery ruled out.

Team director Andy Flower was prompted to suggest Pietersen would therefore be available for the entire English summer, however, the first setback was delivered earlier this month when Pietersen was ruled out of the two-Test series against the Black Caps.

Yesterday's news has further heightened concerns over Pietersen, who missed the final three Tests of the home Ashes series four years ago with an Achilles problem.

England were dealt some good injury news yesterday with seamer Tim Bresnan returning to the County Championship action with Yorkshire for the first time since undergoing elbow surgery.

The Yorkshireman took four for 41, from 20 overs, against Durham at Chester-le-Street after he last week made his playing return in a friendly against Lancashire.

England also expect to have spinner Graeme Swann back to full fitness next month as he also had elbow surgery after he was forced home before the Test series in New Zealand began.