MILAN, Dec 15 (Reuters) - Qatar's sovereign wealth fund is still mulling whether to invest in Monte dei Paschi di Siena's 5-billion euros capital raise, a source close to the matter said.

Qatar Investment Authority could put 1 billion euros in the cash call, sources have said. But it has not made a decision yet, the source said.

"Qatar is still at the window," the source added.

The source also said that Mediobanca , JPMorgan , Credit Suisse and HSBC had arranged a 4.7 billion euro bridge loan for the Tuscan bank's planned bad loan sale.

(Reporting by Paola Arosio, writing by Silvia Aloisi) ((silvia.aloisi@thomsonreuters.com; +39 02 6612 9723; Reuters Messaging: silvia.aloisi.thomsonreuters.com@reuters.net))