Mr Buhari has been in the UK for medical treatment for an undisclosed illness since 8 May.
The plane that transported him is still in London and people have been speculating about the daily cost of keeping the plane in he UK.
Garba Shehu told the BBC that it is normal practice that leaders “are not left to be stranded in foreign lands… there must be a plan for an immediate return”.
Questioned about the cost, Mr Shehu said that the Nigerian government has asked that the daily fee be waived and if that was not possible then only the minimum would be paid.
“Nothing in excess of £1,000,” he said.