An India statement released before play started Friday confirmed Zaheer's hamstring strain and said he was undergoing treatment by the team's physiotherapist.

India are optimistic Zaheer will, at the very least, be fit to bowl come the second innings but, with Lord's bathed in sunshine Friday and conditions for batting improving markedly from Thursday, the course of the match may have been determined by the time he returns.

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The India statement said of Zaheer: "He may be unavailable to bowl (again) in the first innings but is likely to be fit to bowl in the second innings."

Being without the 32-year-old Zaheer for any length of time would be a huge blow to India as he looked a class above fellow seamers Praveen Kumar and Ishant Sharma on Thursday.

And with India having selected just a four-man attack including off-spinner Harbhajan Singh, Zaheer's absence leaves India captain Mahendra Singh Dhoni with few options in the field.

Zaheer removed both England openers, Alastair Cook and captain Andrew Strauss on Thursday.

But when he was off the field, England did not lose a wicket and resumed Friday on 127 for two.

Jonathan Trott was 58 not out and Kevin Pietersen 22 not out.

This match, the 2,000th Test of all time and the 100th between England and India, was also the first of a four-match series.

If England win the series by two clear Tests they will replace leaders India at the top of the ICC's Test Championship table.