Garcia Sabrido, who flew to Cuba last week to examine the 80-year-old leader, said he did not need further surgery but required physical therapy, a strict diet and rest.
"He does not have cancer, he has a problem with his digestive system," he said.
"President Castro has no malign inflammation, it's a benign process in which he has had a series of complications."
John Negroponte, the US director of national intelligence, told The Washington Post on December 15 that "everything we see indicates it will not be much longer ... months, not years".
In Havana, Cuban officials declined to comment on the doctor's statements, saying Castro's condition was a state secret.
But his prognosis was in line with what they have been saying for months.
Raul Castro, the 75-year-old defence minister took over the government temporarily on July 31 when emergency surgery forced his brother to relinquish power for the first time since Cuba's 1959 revolution.