MILAN, March 18 (Reuters) - Italy's Risanamento RN.MI said on Tuesday it had received information about a new legal challenge from a group of companies, owned by the real estate firm's former owner Luigi Zunino, against the decision to sell its Paris properties. The board of the company gave final approval on Friday to an offer worth 1.23 billion euros ($1.7 billion) by Chelsfield/The Olayan Group to sell nine high-end properties in the heart of Paris. ($1 = 0.7180 Euros) (Reporting by Isla Binnie) ((isla.binnie@thomsonreuters.com; +39 02 661 29435; Reuters Messaging: isla.binnie.thomsonreuters.com@reuters.net)) Keywords: RISANAMENTO CHALLENGE/