MILAN, Feb 24 (Reuters) - Milan prosecutors have placed Vivendi chairman Vincent Bollore under investigation for alleged market manipulation over the French group's stake building in Italy broadcaster Mediaset, a source with knowledge of the matter said on Friday.
Bollore was not immediately available for a comment.
In December Milan prosecutors opened a preliminary probe into Vivendi's stake building in Mediaset after the broadcaster's top shareholder Fininvest filed a complaint.
At the time no individual or company was targeted by the investigation which was against unknown persons.
After revealing a 3 percent stake in Mediaset last December, Vivendi has rapidly tightened its grip on the broadcaster to become its second biggest investor after former Prime Minister Silvio Berlusconi's family.
Vivendi has just under 30 percent of Mediaset.
The news of Bollore being put under investigation was first reported by Italian dailies Corriere della Sera and La Repubblica on Friday. (Reporting by Emilio Parodi, additional reporting by Dominique Vidalon in Paris, writing by Stephen Jewkes, editing by Giselda Vagnoni)