MILAN (Reuters) - France's Amundi (>> Amundi S.A.) is the likely winner in the bidding race to buy UniCredit's asset manager Pioneer, beating a consortium led by Italy's post office and Ameriprise Financial (>> Ameriprise Financial, Inc.), two sources close the matter told Reuters on Sunday.

Italy's biggest bank is looking to sell Pioneer and other businesses to strengthen its balance sheet. The lender is set to unveil a strategic plan on Dec. 13 which sources have said will include a share rights issue for up to 13 billion euros (11 billion pounds).

Amundi and UniCredit (>> UniCredit SpA) declined to comment.

One of the sources said Amundi had offered more than 3.5 billion euros, although it was not clear whether this included a 325 million euro cash position held by Pioneer.

The same source mentioned disagreements between Poste Italiane (>> Poste Italiane SpA) and UniCredit over the distribution contract that the buyer would have had to undersign with the lender.

Sources told Reuters on Nov. 25 that Amundi had made the highest offer for Pioneer, and that the Poste-led consortium and Ameriprise were scrambling to stay in the race. Aberdeen Asset Management dropped its bid for Pioneer last month as it considered the price too high.

Pioneer is Europe's sixth-largest asset gatherer and has assets under management of around 225 billion euros.

As investors around the world search for higher returns, asset gatherers have grown rapidly in recent years, making them an appealing target for banks and financial institutions.

(Reporting by Francesca Landini, Paola Arosio, Gianluca Semeraro,; Additional reporting by Maya Nikolaeva in Paris, Writing by Giulia Segreti, editing by Silvia Aloisi)