According to information provided to the BBC, there are "grave concerns" about the deportation of Abu Hamza's son to Turkey.
After traveling to Syria to fight, Sufyan Mustafa, a Londoner, had his British citizenship taken away in 2016.
The 28-year-old is expected to board a flight from the Netherlands to Turkey just before noon on Friday, according to the BBC.
The situation is "very, very worrying," according to his attorney Flip Schüller.
According to him, a deal between Turkey and the Netherlands has led to the deportation of his client, whose father is a well-known hate preacher currently serving a life sentence in a US prison for terrorist offenses.
His legal team worries that he may be extradited to a third country because it is unknown what charges, if any, he will face in Turkey.
Mr. Schüller continued, "Neither his legal team nor the general public have been given the specifics of this agreement.
"The reason the specifics are being kept private causes us great concern. This is incredibly worrying.
The indirect refoulment of my client by Turkey (the forcible return of refugees or asylum seekers to a country where they are likely to face persecution) raises serious concerns.
When Mustafa, also known as Sufean Mostafa Kamal, was 18 years old in 2013, he traveled to Syria and spent the next six years there fighting against Bashir al Assad's government.
In 2016, the UK government revoked his citizenship; Mustafa told the BBC in 2022 that this was done because they believed he was involved in terrorist activity while in Syria.
Mustafa insists that his role was to aid in the protection of the Syrian people and categorically denies engaging in any form of terrorism.
He was taken into custody in Turkey in 2019 and flown to the UK two years later.
He was detained in Amsterdam and transported to the Nieuw Vosseveld high-security prison in Vught.
His attorneys claim that after a legal dispute developed, a deal was eventually reached between Turkey and the Netherlands in August of last year.
They worry that he will be detained in Turkey before being sent elsewhere for deportation.
Mustafa, who was a student in London when he departed for Syria, currently resides in the city with his wife and two sons.
The situation has become increasingly stressful for his family as they wait to find out where he will go and what will happen to him, a family member who asked not to be identified told the BBC. His wife and kids have been extremely distressed by it.
When will we see Daddy again? is a question that his son keeps asking.
The question is challenging for them to answer. That the kids should endure this suffering is unfair. A fair trial is all that the family requests.
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