The man due to be the next Governor of Bermuda was attacked in London by a black man wearing a hoodie. Doctors say he will lose sight in one of his eyes.
Mr Fergusson, who lost a small amount of cash in the mugging, works for the Foreign Office and is due to take up the post of governor of Bermuda.
The governor acts as the Queen’s official representative in Bermuda.
A spokesman for the FCO said Mr Fergusson had had surgery and lost the sight in his left eye.
He said: “He was supposed to take up his next post in May and that is still the plan.”
Mr Fergusson, who lives in Lambeth, south London, with his wife Margaret, previously served as governor of the Pitcairn Islands, as well as high commissioner to New Zealand and Samoa.