Will Pooley, 29, was discharged from the Royal Free Hospital in north-west London two weeks ago where he received treatment in a special isolation unit.
Both Mr Pooley and the new victim, who has not been named, are believed to have worked together in Sierra Leone.
The Foreign Office said it had arranged a replacement passport within 24 hours.
As a survivor of the disease, Mr Pooley could help the victim recover by donating his blood which will now contain natural antibodies that can help protect against Ebola.
Mr Pooley is thought to have flown to Atlanta at the weekend after the Foreign Office issued him with an emergency passport.
His original passport was burned along with other belongings as a precaution to stop the virus from spreading.
The Foreign and Commonwealth Office (FCO) said in a statement: "Following a request from his family, the FCO Consular Team and the UK Passport Office worked together to get a replacement passport to Will Pooley within 24 hours, this enabled him to fly out to the US immediately and potentially assist with the treatment of an Ebola victim."
Infectious diseases specialist Dr Aneesh Mehta, one of five doctors working at a specialist unit in Atlanta, said the team were looking at all treatment options for the latest patient.
He said: "We believe the supportive care - allowing the body to heal itself and supporting it through that process - is the mainstay of therapy, as is true for any infectious disease. If we have therapeutic options, we'll evaluate those."
Ebola is transmitted through sweat, blood and saliva.
The World Health Organisation says that more than 2,500 people have been killed by the latest outbreak in west Africa, where the death rate stands at 90% if it goes untreated.
A British nurse who recovered from Ebola has travelled to the US to donate blood to try to save the life of another victim of the virus.