"Sami wrote me a letter in his handwriting that he is diabetic now, he suffers weakness of sight, high blood pressure and rheumatism."
Al-Hajj, originally from Sudan, was arrested in Pakistan in December 2001 by Pakistani intelligence officers while travelling near the Afghan border.
Despite holding a legitimate visa to work as a cameraman for Al Jazeera in Afghanistan, Al-Hajj was handed to the US military in January 2002 and sent to Guantanamo Bay in Cuba for allegedly having ties to al-Qaeda.
He has never been charged.
Hopes that Al-Hajj would be released last August on the condition that he remain in his country of origin proved unfounded.
The news follows the sixth anniversary of the opening of the notorious US detention centre.
Protesters around the world staged rallies on Friday calling for the closure of Guantanamo Bay.
Eighty-one demonstrators were arrested outside the US supreme court in Washington DC.
Activists from Amnesty International, the human rights organisation, and others also gathered in cities such as London, Sydney, New York and Manila.
The US has suggested it wants to close Guantanamo, where 275 detainees are held including about 60 who US military panels have cleared for release or transfer.
Zachary Katznelson, senior counsel at Reprieve, an organisation that provides legal assistance to prisoners, said the US approach to those imprisoned in Guantanamo is inconsistent.
"On the one hand, [the US is] continuing to try and paint the people in Guantanamo, even though they haven't been charged and they haven't been tried, as vicious terrorists," he said.
"And at the same time [they are] trying desperately to get other countries to take them in."
Some countries have refused to accept prisoners that Washington no longer wants to hold and in some cases, detainees themselves do not want to be sent back because they fear they will be persecuted.
Since the prison's opening, four prisoners have committed suicide by hanging - three in June 2006 and one in May 2007.
A fifth prisoner died of colorectal cancer in December 2007, the first to die of natural causes.
Al-Hajj is one of about 20 prisoners who have carried out hunger strikes in protest of their imprisonment and treatment at the US jail.