It is believed that Foreign Secretary Boris Johnson is also very unlikely to attend the Cuban revolutionary leader’s funeral.
The Government is currently in discussions with Cuban officials about the “appropriate level of attendance”, with minister for the Americas Sir Alan Duncan a potential representative.
Mrs May’s spokeswoman told a Westminster briefing: “The final arrangements are still being made and we are in contact with officials there about the appropriate level of attendance.
“I’m not expecting the Prime Minister will be attending.”
It is understood that Labour leader Jeremy Corbyn has not yet received an invitation to the funeral, although it is unclear whether he will in future.
Mr Corbyn has been criticised for saying that “for all his flaws”, Castro will be remembered as a “champion of social justice”, with an outcry over the communist regime’s human rights abuses and lack of democratic accountability.
Asked about Mrs May’s views on Castro, her spokeswoman said: “The Prime Minister shares the view set out by the Foreign Secretary this weekend that he was marked out as a historic, if controversial figure, and we now want to look to the future, how we can work with the government of Cuba on a wide range of priorities, including human rights.”
Nine days of national mourning were declared in Cuba after Castro’s death at the age of 90.
His ashes are due to be taken across Cuba from the capital Havana to the city of Santiago, where they will be laid to rest on Sunday, along the route taken by his rebel army when he swept to power.