Writing in Cuba's state newspaper, Granma, Mr Castro insisted that he is consulted on every government decision.
The article did not suggest when Mr Castro, who has not been seen in public for over a year, could return to power.
"Raul himself has been entrusted with making sure that every important decision, during the period that I have been recovering, was decided after consulting with me," he wrote.
"What am I going to do? I will fight ceaselessly as I have done all my life," he said.
For the first time in 48 years, Mr Castro did not put in an appearance at the country's National Rebellion Day celebrations last week.
Secrecy surrounding his condition has fuelled to rumours about the extent of his health problems and his eventual political future.
However, Cuban officials have repeatedly said he will eventually resume office.