By Gianluca Semeraro and Maria Pia Quaglia
MILAN, Nov 3 (Reuters) - U.S. financial services companyAmeriprise Financial has joined the race to buy assetmanager Pioneer Investments, which has been put on the block byItaly's biggest bank UniCredit, two sources close tothe matter said on Thursday.
The Minneapolis-based company, which controls ThreadneedleAsset Management, joins four other bidders that are expected topresent binding offers for Pioneer by Nov. 10, the sources said.
Ameriprise and UniCredit declined to comment on the issue.
Europe's biggest asset manager Amundi and anItalian consortium led by Poste Italiane are seen asfrontrunners in the race.
Australia's Macquarie and British group AberdeenAsset Management are also interested in the unit.
The sale of the asset gatherer is part of a broader effortby UniCredit to boost its capital. Led by its new CEOJean-Pierre Mustier, the bank is due to unveil a new strategicplan on Dec. 13.
The offers will likely value Pioneer between 3.2 billion and3.4 billion euros ($3.8 billion), another source said.
Poste Italiane has had contacts with both Aberdeen andMacquarie over joining forces to buy Pioneer but the talks haveso far led nowhere, a fourth source said.
One of the sources said a further extension of the deadlinefor presenting binding offers could not be ruled out.
($1 = 0.9013 euros) (Additional reporting by Francesca Landini)