The Serie A football club is owned by Fininvest, the family holding of former Italian prime minister Silvio Berlusconi.
Berlusconi and Bee signed a pre-sale agreement in August and a final deal was supposed to be inked by the end of September.
The sources did not elaborate on the reasons for the holdup, but said Berlusconi and Bee had spoken over the phone on Monday to discuss the state of the matter.
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"It's pretty obvious that there will be no closure by the end of the year," one of the sources said, adding that talks will pick up in January, when Bee is also expected to come to Italy.
(Reporting by Elvira Pollina, writing by Agnieszka Flak, editing by Francesca Landini)
