"I was prevented from visiting the president in my capacity as a lawyer although I had a judicial permit" Osama wrote on his Facebook account.
"We assume – because of this arbitrarily measure from the coup authorities – that the president is not inside Burg al-Arab prison and is being held at an undisclosed location," he argued.
Anadolu Agency could not get an immediate comment from Egyptian prison authorities on Osama's allegations.
It was the third time that members of Morsi's family were barred from visiting the jailed leader since he managed to convey a message to the Egyptian people last month via lawyers who had visited him in jail.
Morsi was flown to Alexandria's maximum-security Burg al-Arab Prison earlier in November after appearing in court for the first time on charges of inciting the murder of demonstrators outside Cairo's Ittihadiya presidential palace late last year.
Morsi has refused to recognize the trial's legitimacy, telling the presiding judge at one point that he still represented Egypt's legitimate president.
Morsi's supporters, who describe his ouster by the July on July 4 as a military coup, insist that charges against him are politically motivated.
Trial proceedings are slated to resume on January 8.