MARINA DI PIETRASANTA, Italy (Reuters) - Italian Prime Minister Matteo Renzi said on Sunday he was not worried about the situation at Italian lender Banca Monte dei Paschi di Siena <BMPS.MI>.

It emerged last week Monte dei Paschi's CEO Fabrizio Viola was under investigation for alleged false accounting and market manipulation in a case involving derivatives trades.

The investigation hits the Tuscan lender as it readies a 5 billion euro stock sale to strengthen its balance sheet after emerging as the weakest bank in Europe in July stress tests.

"Not at all," Renzi said when asked if he was concerned for the lender on the sidelines of a public interview.

(Reporting by Silvia Ognibene, writing by Stephen Jewkes)