"The visit will make preparations for his return, should the ongoing US review into Guantanamo Bay detainees confirm a decision to release him," an FCO statement said.
"The team includes a doctor, who would take part in any return, so that he may assess Mr Mohamed's condition himself and report back."
Mohamed has been on hunger strike since early January, according to his US military lawyer. He has lost so much weight that his health is at risk and he is being force fed, Lieutenant-Colonel Yvonne Bradley said on Wednesday.
"I was totally shocked by his condition," she told members of Britain's parliament and the media, saying she had last seen him on January 28. "I have serious concerns that he could die."
The visit follows a move by US President Barack Obama to prioritise a review of Mohamed's case and could lay the ground for Mohamed, who says he was tortured by foreign agents while in US detention, to be returned to Britain.
Mohamed, an Ethiopian national, was arrested in Pakistan in April 2002. He says he was then flown to Morocco on a CIA plane and held for 18 months, during which he says he was repeatedly tortured, including being cut with a knife.
Morocco has denied holding him. He was transferred to Afghanistan in 2004 and later moved to Guantanamo, US authorities have said. Washington denies that he was subjected to rendition or torture.
One of Obama's first acts as president was to announce that Guantanamo, widely viewed as a stain on the United States' human rights record, would be shut down.
The prison was set up at a US military base in Cuba to hold captives from the "war on terror" launched after the September 11, 2001, attacks on the United States.
Mohamed's case has attracted widespread publicity in Britain because US legal authorities have fought to prevent evidence being released that his lawyers say shows he was tortured. The evidence is contained in documents held in Britain.
Britain's high court ruled last week the evidence should not be released as it could lead to reduced intelligence cooperation with the United States and prejudice Britain's national security.