The individual has been detained by Geneva police and his home searched, the public prosecutor for the canton (region) of Geneva told AFP, without giving further details.
The Zurich daily Tages Anzeiger earlier reported that the banker, working for Credit Suisse, had exceeded his authority, losing more than 50 million Swiss francs ($50 million) for a wealthy client.
The daily Le Temps put the losses at closer to 100 million francs and said the client was a Georgian oligarch.
Two other clients have lost 70 million francs and are preparing to file a criminal complaint against Credit Suisse, Le Temps said.
In all three cases, an investment was made in a US pharmaceutical firm, Raptor, whose stock value plummeted after it failed to get regulatory approval in the United States for one of its medications, the French-language daily said.
In its financial report for the third quarter of 2015, Credit Suisse stated under a section on “customer account matters” that some clients have raised concerns about a “former relationship manager” whose management of their accounts led to investment losses.
“A few clients have claimed that a former relationship manager in Switzerland has exceeded his investment authority in the management of their portfolios, resulting in excessive concentrations of certain exposures and investment losses,” says the report, released in October 2015.
“Credit Suisse AG is investigating the claims, as well as transactions among the clients,” it said.