Megrahi was the only person convicted of the 1988 bombing of Pan Am flight 103 over Lockerbie, Scotland.
Andrew Fraser, a chief medical examiner at the Scottish Prison Service, said Megrahi had only three months to live. Fraser is not a cancer specialist, however, and had no direct contact with doctors examining the former Libyan intelligence officer, London's Telegraph newspaper reports.
Zac Latif, a urologist who the Telegraph said treated Megrahi, said the assessment made by Fraser was "a bit odd."
"I don't know how he made the decision of three months," he added.
U.S. lawmakers, outraged over the BP oil spill in the Gulf of Mexico, have called on Scottish officials to release the medical records that led to their decision to release Megrahi.
Libyan doctors said Megrahi could live another 10 years.
BP, for its part, is scheduled to start drilling for oil off the Libyan coast later this year. The company denied any links to Megrahi but acknowledged a role in prisoner transfer negotiations.