Shakil Afridi's lawyer Samiullah Afridi went abroad after militants threatened to kill him.
Though sources didn't identify where he had fled to, some media reports said it was Dubai.
The lawyer is likely to have fled yesterday, the time since when his phone remained unreachable. He did not voice any fear or threats when PTI spoke to him two days ago.
Afridi, who was arrested immediately after the May 2, 2011 operation by US commandos that killed Laden, was convicted for treason over alleged ties to militant group Lashkar-e-Islam.
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Frontier Crimes Regulation Commissioner Sahibzada Mohammad Anees ruled that a judge in the tribal belt had exceeded his authority when he handed down the sentence last year.
He had ordered a fresh trial and had said it would be heard by the Political Agent.
Samiullah had been representing the doctor from day one.