Surgeon 'flew in to treat Castro'
The Cuban government has not commented on any aspect of the report.
The surgeon, Dr Jose Luis Garcia Sabrido, is an expert on intestinal ailments, particularly cancer.
President Castro temporarily stepped down from power last July and issued a statement saying he had undergone an operation to stop intestinal bleeding.
Although his health is a state secret, Cuban officials have said that he is not suffering from cancer or any terminal illness, and that he is recuperating.
The Barcelona-based newspaper says that Dr Garcia Sabrido flew to Havana on a jet chartered by the Cuban government.
Citing Spanish medical sources, it reports that the surgeon brought with him equipment which is not available in Cuba.
It says he came to give his professional advice on whether President Castro should undergo further surgery.
Dr Garcia Sabrido is understood to have been in Havana just last month - on that occasion to take part in an international conference on surgery.
According to the programme for the event, he gave two lectures. One was on peritoneal cancer - a cancer of the lining of the abdomen. The other was on colonic cancer.
US claims denied
Since Mr Castro temporarily stood down from power almost five months ago, there has been no shortage of speculation as to what he might be suffering from.
Unnamed US officials have told American media that it is cancer, possibly in its terminal stages.
But earlier this month, Venezuelan leader Hugo Chavez strenuously denied that his long-time friend and ally was suffering from the disease.
Cuban government officials, including the country's foreign minister, gave the same message to a visiting group from the US Congress last week.
And on Friday, Raul Castro, the acting President of Cuba, assured delegates at the country's national assembly that his brother was progressing in his recovery.
Source: BBC News