Kevin Pietersen's departure from Pakistan last night is the latest body blow for England on a tour which has been beset by injuries and defections.

Pietersen is the third key player to suffer a tour-ending injury - captain Michael Vaughan and left-arm spinner Ashley Giles have already had operations back in England - while Andrew Strauss missed the third Test to attend the birth of his first child.

It was obvious from his frenetic and eventually curtailed performance in Sunday's one-day defeat against the hosts at Lahore's Gaddafi Stadium that Pietersen was significantly hampered by a rib injury which was at first thought to be minor.

A cortisone injection was due to be administered in the hope the destructive middle-order batsman could be nursed through the remaining three matches of this tour. But England had to accept he was unfit to continue a series which stands at 1-1 and would not travel with the squad for the next fixture in Karachi tomorrow.

Pietersen has reluctantly accepted the verdict of England's chief medical officer Dr Peter Gregory.

''It's very disappointing to be leaving the England team because I was looking forward to a strong one-day series,'' he said.

''I hate missing matches, but despite trying to play the first couple of one-day games the pain was just too great.''

The South Africa-born batsman hopes to be fully fit in time to join England's three-Test and seven one-day international tour of India, which starts in mid-February.

''I certainly wouldn't want to let my team-mates down because of injury - whether it is with the bat or in the field - so the only choice available is to rest the injury with a view to a full recovery in time for India.''

It is thought to be a previously undiagnosed problem which was aggravated when he dived in fielding practice before England's first one-dayer in Lahore on Saturday.

For the England medical team, it is the latest in a series of difficulties which have characterised England's tricky tour.

Vaughan's knee dominated the build-up to the first Test, then Giles' hip ruled him out of the final match of a series which was lost 2-0.

Both men were, like Pietersen, suffering recurrences of previous injuries.

For England it was an unwelcome echo of a problem which once seemed to afflict them at every turn yet last summer barely entered the equation at all as they went through an entire Ashes series with only one change to their team.

Dr Gregory, still hoping Vaughan and Giles will be fit for the second leg of England's winter, is similarly optimistic about Pietersen.

''A stress lesion of this nature is likely to require four to six weeks' rest, but it is expected that Kevin will make a full recovery in time for the tour to India in March next year,'' he said.

''Scans taken after the first one-day match showed no fracture but demonstrated the stress lesion, and despite passing a fitness test before the second one-day match, Kevin suffered intolerable pain throughout.''

News of Pietersen's short-term unavailability comes only a day after England discovered they are to lose another key figure permanently.

It was confirmed yesterday that bowling coach Troy Cooley has accepted an offer to work in a similar capacity for his native Australia.

His absence will be felt especially keenly by England's chief coach Duncan Fletcher, who made no attempt yesterday to disguise his regret at losing someone he sees as an important contributor to the team's success in recent years.

''I think it's a huge blow to us,'' he admitted.

''Just as we've achieved something, he's on his way. It's a huge disappointment as far as I'm concerned.''

Fletcher expects it will be difficult to replace Cooley, a man he saw as an integral part of England's planning for years to come.

''I wished him well. It's his decision; he's done a tremendous job for us,'' he said.

''He fitted in well and really was a good coach. I was hoping we could go through to the World Cup with him.''

Cooley's attributes were many, according to a like-minded Fletcher.

''It's taken me some time to put together what I believe is a really good unit, good management team with the right personalities,'' he recalled.

''You go on tours around the world and you have to have individuals who get on with each other and can relate to each other.

''He has very similar ideas to me, and I realised when I first met him he was an individual I wanted to get on board quickly.''