He said he hoped Castro would recover but admitted the situation was difficult. Chavez also said Castro was "immortal" like legendary guerrilla leader Che Guevara, who was killed in Bolivia in 1967.
A recent Spanish press report said Castro was gravely ill following three failed operations.
The 80-year-old Castro has not been seen in public since he underwent intestinal surgery in late July 2006. He has transferred power temporarily to his 75-year-old brother, Raul.