Gul went off the fielding after bowling just two overs in the MCC versus Rest of the World match at Lords yesterday.
"He went off after bowling two overs and fielded only for a while. We have heard that he might have aggravated the same right knee on which he had surgery last year," a source close to the selectors told PTI.
Gul, who is Pakistan's most experienced pace bowler in the present team, has faced problems with his knee since last year and even after making a comeback last October in the series against Sri Lanka in the UAE there are doubts over his ability to bowl long spells without breaking down.
Gul underwent the knee surgery in May last year in Australia after he broke down during the tour to South Africa.
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"Gul has struggled and bowled with the knee problem for sometime now which is why he was sent to have the surgery. He figures prominently in our future plans leading up to the World Cup so obviously the selectors are concerned with him bowling just two overs at Lords," the source said.
The ability of Pakistan's other pacer Mohammad Irfan to bowl long spells has also been reviewed by the national selectors and both were unlikely to feature in the coming Test series against Sri Lanka.