In power since 1959, a message attributed to Fidel Castro said he would be out for "several weeks of rest" following an operation to stem intestinal bleeding.
Raul still hasn’t been seen in public even though he took over from his ailing brother Fidel three days ago.
Instead of a public speech by Raul, an old address on the legitimacy in Cuba's leadership which he gave on July 1 was re-run in the Communist Party newspaper, Granma.
Cuba's enemy, Raul said in reference to the United States, "knows that the special trust the people put in the main leader of a revolutionary government is not passed on as if it were an inheritance to those who in the future may hold the country's top leadership positions.
"There is only one commander-in-chief of the Cuban Revolution, and it is the Communist Party," he was quoted as saying in the front-page Granma story.
Some analysts saw the recycled address as the party's response to questions about Raul's lack of visibility.
The United States, meanwhile, issued its first statement Thursday critical of the way power was passed on from Fidel to his brother.
"The imposition of Raul Castro denies the Cuban people of their right to freely elect their government," said State Department spokesman Sean McCormack.
"We are ready to help Cuba through a democratic transition and are prepared to rapidly provide substantial humanitarian relief to support a genuine transition," Mr McCormack said.
For many people on the street of Havana, no news from the man now wielding Cuba's power, who leads the state, government, 50,000-man armed forces and Communist Party, was not necessarily good news.
Regime watchers are not deeply surprised by Raul taking his time and keeping a low profile.
But the uncertainty has helped fuel speculation about whether Cuba might move toward some kind of transition, stay essentially the same or even see the government take a harder line.
On the street, many people said they were not that familiar with Raul, who was seen as a hardliner early in the communist regime.
He is now said to admire China's embrace of communism and capitalism. He led pragmatic reforms such as opening up to tourism.
Fidel Castro, who turns 80 on August 13, has been heard from only in a statement attributed to him late Tuesday. He was last seen in public July 26.
His sister Juanita, a drugstore owner in Miami, told US media she had been told her brother Fidel was out of intensive care following surgery.