Umar was called back by the PCB from the West Indies after he fell unconscious after a seizure on a flight from Trinidad to Antigua during the Caribbean Premier League.
He was taken to a hospital in Antigua where doctors, after examining him in detail, sent a report to the PCB.
"They sent the alarm bells ringing in the board when the report said that Umar had 35 to 50 percent probability of suffering seizures again in his lifetime and such seizures are normally associated with epilepsy," an official source in the board told PTI.
The source made it clear that after reading the report, the board decided that Umar should undergo further detailed scans and tests in Pakistan.
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"He has so far been examined by two top neurologists in Lahore and Karachi. He was sent to Karachi for a second examination with neurologist Dr Nadir because there are more facilities available for all possible scans related to his condition," the source said.
He said Dr Nadir would be sending his report to the board today.
He pointed out that when a player was given medication and therapy his concerned home board had to first get all clearance from the ICC in accordance with their anti-doping policy so that he does not end up testing positive in any doping test.