Klasnic returns to Bolton
The 30-year-old told Bolton's website it was an easy decision to return to the club after scoring eight league goals in the 2009/10 campaign.
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"I spoke to the manager - he wants to work with me and I want to work with him," said Klasnic, who returned to French club Nantes at the end of the loan deal.
The Hamburg-born player won the Bundesliga with Werder Bremen in 2003/04 and featured in the Champions League for the German club.
Klasnic is the fourth player to sign for Bolton during the close season, joining Bulgarian midfielder Martin Petrov, Robbie Blake and young Spanish defender Marcos Alonso.