The Cuban leader is set to miss the celebrations in Havana marking his 80 years.
“The Cubans were empathetic, and I believe them, that Fidel does not have cancer and that the illness he does have is not terminal,” Delahunt told the Times after returning to Washington.
If Castro reappears, “this will not be Fidel sitting at his desk”, Delahunt said. “This will be Fidel Castro is alive and recovering.”
Castro did not appear at celebrations of his 80th birthday this month, prompting rumours that he had died or was near death.
The 10-member US congressional delegation, was the largest to go to Cuba since Castro’s 1959 revolution.
The three-day visit was aimed at improving ties between Havana and Washington. But the delegation’s efforts to launch a new dialogue with Cuba on the assumption that Castro was out of the picture were rebuffed by officials who insisted he was recovering.
Cuba has closely guarded information on Castro’s medical condition. But his closest ally, Hugo Chavez, the Venezuelan president, has said that although Castro does not have cancer, he is fighting a “great battle” against a “very serious” illness.