* 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 forUniCredit's fund management arm Pioneer as the auctionfor 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 and anItalian consortium led by Poste Italiane are seen asthe frontrunners after submitting the highest non-binding offersin September, the sources said.
But two other companies, Australia's Macquarie andBritish group Aberdeen Asset Management, are alsointerested in Pioneer and they're currently performing duediligence on the business which has over 220 billion euros ($246billion) of assets under management, the sources said.
UniCredit, Amundi, Poste Italiane, Macquarie and Aberdeendeclined to comment.
UniCredit seeks to raise around 3 billion euros from thesale of Pioneer, a deal seen as crucial to plug a gap in itscapital requirements estimated to be as big as 8 billion euros.
Italian insurer Assicurazioni Generali, thecountry's largest asset manager, has been unable to make acompetitive offer amid a lack of shareholder support, thesources said.
French insurer Axa has also failed to progress tothe second round of the auction, the sources said, while Frenchbank Natixis has been given the opportunity to sweetenits non binding offer, which came close to meeting UniCredit'sexpectations but was lower than the other four bids.
Assicurazioni Generali and Axa declined to comment andNatixis was not immediately available for comment.
Unicredit's French boss Jean-Pierre Mustier, appointed inJuly, will unveil a new strategic and capital-boosting plan forthe Italian bank on Dec. 13. He will not select the final buyerfor Pioneer until after a referendum on Prime Minister MatteoRenzi's flagship constitutional reform on Dec. 4.
The fate of the Italian government likely hinges on theoutcome of the referendum, and political instability in case ofa 'No' vote could overshadow UniCredit's fund-raising efforts.
APPETITE FOR DEALS
UniCredit is currently conducting a wide-ranging review ofits businesses with a view to selling more assets and reducingthe size of any share issue.
Other big European banks who run asset management units suchas Deutsche Bank are also expected to review optionsfor those businesses which appeal to industry rivals as well asprivate equity funds, bankers and analysts said.
For the likes of Amundi, Aberdeen and Anima Spa --an Italian fund manager which has teamed up with Poste Italianeand state-backed bank Cassa Depositi e Prestiti -- the purchaseof Pioneer offers an opportunity to build scale across severalinternational markets, including the United States.
Amundi, which has almost $1 trillion of assets undermanagement, was created from the merger of the asset managementarms of French banks Credit Agricole and SocieteGenerale in 2010 and is now valued at 7.5 billioneuros, having been listed on Euronext Paris last November.
Analysts expect a flurry of deals among mid-sized assetmanagers who need to streamline operations and diversify inorder to protect profits as clients push fees down andregulators ramp up scrutiny of fund managers' practices.
London-based asset manager Henderson Group agreedto buy U.S. rival Janus Capital Group Inc on Monday inan all-share $6 billion deal to cut costs and boost profits.
($1 = 0.8957 euros) (Additonal reporting by Maya Nikolaeva; Editing by RachelArmstrong and Susan Fenton)