The chief executive of Pioneer Investments, one of Europe's largest asset managers with €170bn ($260bn) under management, has unexpectedly announced his departure from the company with no successor lined up to take over.

A spokesman for UniCredit, the Italian bank that owns Pioneer, said: "UniCredit Group communicates that Dario Frigerio, chief executive officer of Pioneer Investments and deputy general manager of the group, is leaving the company to pursue new professional opportunities.