India's ambitious designs of making a comeback from 0-2 down in the four-Test series against England suffered a setback with the news that its spearhead Zaheer Khan will miss the remainder of the tour.
The injured left-armer faces 14 to 16 weeks of rehabilitation, the BCCI said in a release, and will be replaced in the squad by R.P. Singh, who last played a Test in April 2008.
Zaheer strained his hamstring on the first day of the first Test at Lord's. According to the BCCI, the 32-year-old is suffering from a right ankle impingement in addition to a recurrent right hamstring strain.
Zaheer will undergo ankle surgery before an intensive rehabilitation programme for both the hamstring and the ankle.

History of injuries
Zaheer, like several fast bowlers, has had a history of injuries. But in recent years he had developed an understanding of just what his body needed. His ability to manage his body through various niggles was instrumental in his becoming India's most vital bowling performer, both home and away.
But the ankle problem, for which he has now decided to go under the knife, prevented him from touring the West Indies and from maintaining optimal fitness. When he arrived in England, he looked less than match-fit. As is often the case with leg injuries, one leads to another because the body is trying to bear weight differently.
After walking off the field in the first Test, he has attempted to nurse his body back into bowling health. He had light training sessions, and the practice match against Northamptonshire here was seen as a test of his fitness.
He bowled three overs off a full run-up before returning to the dressing-room.
Zaheer's departure leaves the attack without its bowling leader. R.P. Singh's strike-rate of 58.2 and average of 39.10 capture his qualities as a bowler: a left-armer who can produce magic balls, but can leak runs in between.
Sreesanth is similar. In both cases, their fuller length, which allows them to swing the ball, makes them easier to score runs off if there's no movement. R.P. Singh shone here in England in 2007 and bowled magnificently in the victory against Australia in 2008. But the 25-year-old went wicket-less in the home series against South Africa in 2008 and hasn't played for India since.
Zaheer is the third cricketer — after Harbhajan Singh and Yuvraj Singh — to leave the squad because of injury. He will be missed the most.