Silvio Berlusconi served as Italy's prime minister four times. Photo: AFP
The 86-year-old, whose media empire has made him a billionaire, is being treated in a cardiac unit of Milan's San Raffaele hospital.
There has been no official comment on his condition, but the source's diagnosis of leukaemia, which is a cancer of the blood cells, confirmed a report in the Corriere della Sera daily.
Berlusconi's Forza Italia party is part of Prime Minister Giorgia Meloni's right-wing coalition, though the former prime minister does not have a role in government.
"I spoke this morning with Professor (Alberto) Zangrillo (Berlusconi's personal doctor) and he told me that Berlusconi spent a quiet night, his condition is stable," Foreign Minister and Deputy Prime Minister Antonio Tajani told RAI state television.
Tajani, a long-time Berlusconi ally within Forza Italia, noted Berlusconi had survived a series of health problems.
"We all want to be optimistic and we hope that the lion will return soon to take charge of the party. He's our political leader and of course he never gives up," Tajani told the broadcaster.
The party subsequently released a statement saying Berlusconi had spoken in the morning to senior Forza Italia allies and urged "maximum commitment" in parliament. "The country needs us," he was quoted as saying.
Enduring influence in Italy
Berlusconi, who made his fortune from commercial television, has suffered repeated bouts of ill-health in recent years and came out of the same hospital just last week after being treated for a few days.
"There is obviously concern.. (He) is alert but not in a position to deal with every situation," Paolo Barelli, leader of Forza Italia in the lower house of parliament, told Italian radio.
Berlusconi stepped down as prime minister for the last time in 2011, weighed down by sleaze and scandal, including his notorious "bunga bunga" parties, as Italy came close to a Greek-style debt crisis.
But he returned to the Italian Senate after a national election last September and there is no obvious successor as leader of his party.
As well as his enduring influence on Italian politics, Berlusconi's Fininvest family holding group retains control of the MediaForEurope broadcast business. His son Pier Silvio Berlusconi is chief executive of the company.
Berlusconi built Italy's biggest commercial TV network and gained an international profile as owner of European soccer champions AC Milan before entering politics in 1994, when the previous political class was brought down by a corruption scandal.
His health has deteriorated in recent years. He had heart surgery in 2016, has also had prostate cancer, and has been repeatedly admitted to hospital since contracting Covid-19 in 2020.
- Reuters