The Muslim Council of Britain said its delegates would be pressing junior Home Office minister Hazel Blears to let the men have medical attention immediately on their return, which is expected on Tuesday.
Iqbal Sacranie, secretary-general of the council, was due to meet Blears along with with representatives from the Muslim Safety Forum and the Muslim College, a spokesman for the council said.
The detainees, who have been held without trial at the centre for terrorism suspects for up to three years, were "heavily traumatised" and "possibly tortured" and would require swift care, spokesman Inayat Bunglawala said.
Mental health fears
The Pentagon first announced on January 11 that Moazzam Begg, Martin Mubanga, Richard Belmar and Feroz Abbasi would be freed from the military-run prison in the near future.
Britain's Foreign Secretary Jack Straw has left open the possibility that the four British detainees will be questioned by police on their return, and potentially charged under domestic anti-terrorism legislation.
The country's most senior police officer, Metropolitan Police Commissioner Sir John Stevens, has been tasked with assessing whether the men should be charged, a sign of how sensitive the issue is, the Guardian newspaper reported on Monday.
Begg said his son is likely to be
questioned by police on arrival
Human-rights campaigners and Muslim groups have campaigned relentlessly for the men - the last British nationals held at Guantanamo Bay - to be freed.
The father of one of the four detainees said at the weekend that he expected his son to be freed on Tuesday.
"The only thing I know is that he's coming (home) Tuesday," Moazzam Begg's father Azmat Begg told Britain's domestic Press Association news agency.
"He will be coming to England to a military base, most probably RAF Northolt (northwest of London), and be taken from there to a police station, maybe Paddington Green (in west London)."