* Amundi and Poste-led consortium seen as frontrunners
* Macquarie and Aberdeen Asset Management also in the race
* Natixis offered last chance to sweeten non-binding offer (Adds context on bidders, industry consolidation)
By Pamela Barbaglia
LONDON, Oct 4 (Reuters) - Four bidders are vying for UniCredit's CRDI.MI fund management arm Pioneer as the auction for the $3.35 billion unit moves to the second round of bidding, two sources familiar with the matter said on Tuesday.
Europe's biggest asset manager Amundi AMUN.PA and an Italian consortium led by Poste Italiane PST.MI are seen as the frontrunners after submitting the highest non-binding offers in September, the sources said.
But two other companies, Australia's Macquarie MQG.AX and British group Aberdeen Asset Management ADN.L , are also interested in Pioneer and they're currently performing due diligence on the business which has over 220 billion euros ($246 billion) of assets under management, the sources said.
UniCredit, Amundi, Poste Italiane, Macquarie and Aberdeen declined to comment.
UniCredit seeks to raise around 3 billion euros from the sale of Pioneer, a deal seen as crucial to plug a gap in its capital requirements estimated to be as big as 8 billion euros.
Italian insurer Assicurazioni Generali GASI.MI , the country's largest asset manager, has been unable to make a competitive offer amid a lack of shareholder support, the sources said.
French insurer Axa AXAF.PA has also failed to progress to the second round of the auction, the sources said, while French bank Natixis CNAT.PA has been given the opportunity to sweeten its non binding offer, which came close to meeting UniCredit's expectations but was lower than the other four bids.
Assicurazioni Generali and Axa declined to comment and Natixis was not immediately available for comment.
Unicredit's French boss Jean-Pierre Mustier, appointed in July, will unveil a new strategic and capital-boosting plan for the Italian bank on Dec. 13. He will not select the final buyer for Pioneer until after a referendum on Prime Minister Matteo Renzi's flagship constitutional reform on Dec. 4. fate of the Italian government likely hinges on the outcome of the referendum, and political instability in case of a 'No' vote could overshadow UniCredit's fund-raising efforts.
APPETITE FOR DEALS
UniCredit is currently conducting a wide-ranging review of its businesses with a view to selling more assets and reducing the size of any share issue. big European banks who run asset management units such as Deutsche Bank DBKGn.DE are also expected to review options for those businesses which appeal to industry rivals as well as private equity funds, bankers and analysts said.
For the likes of Amundi, Aberdeen and Anima Spa ANIM.MI -- an Italian fund manager which has teamed up with Poste Italiane and state-backed bank Cassa Depositi e Prestiti -- the purchase of Pioneer offers an opportunity to build scale across several international markets, including the United States.
Amundi, which has almost $1 trillion of assets under management, was created from the merger of the asset management arms of French banks Credit Agricole CAGR.PA and Societe Generale SOGN.PA in 2010 and is now valued at 7.5 billion euros, having been listed on Euronext Paris last November.
Analysts expect a flurry of deals among mid-sized asset managers who need to streamline operations and diversify in order to protect profits as clients push fees down and regulators ramp up scrutiny of fund managers' practices.
London-based asset manager Henderson Group HGGH.L agreed to buy U.S. rival Janus Capital Group Inc JNS.N on Monday in an all-share $6 billion deal to cut costs and boost profits. = 0.8957 euros) (Additonal reporting by Maya Nikolaeva; Editing by Rachel Armstrong and Susan Fenton)