The holding company, Fininvest, declined to comment.
Berlusconi, who leads the biggest political party on Italy's centre-right, denied a report on Saturday in La Stampa newspaper which said prosecutors had opened an investigation into alleged money laundering during the sale.
Milan's chief prosecutor Francesco Greco also said no investigation had been opened into the sale.
The four-times prime minister sold the club last April for 740 million euros (657.76 million pounds) and stepped down from his role as president that he had held for more than 30 years.
No investigation has been opened, the sources said on Monday, but the finance police delivered a report of around 10 pages to the prosecutor's office before Christmas, they said.
Financial institutions are obliged to notify the Bank of Italy of transactions in which there is "reasonable cause to suspect" financial crimes such as money laundering have been committed or attempted.
The central bank then sends these notifications to the finance police, which compiles a report that is sent to a prosecutor, who must decide whether to open a probe.
The report regarding the AC Milan sale contained three indications of suspicious operations, known in Italian by the acronym "SOS", the sources said.
Marina Berlusconi, the politician's daughter and chairman of Fininvest, said in a statement on Saturday it had "behaved absolutely transparently and correctly" throughout the negotiations for the sale of the club.
(Reporting by Manuela D'Alessandro,; Writing by Isla Binnie; Editing by Richard Balmforth)
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