LONDON, March 12 (Reuters) - The GFG Alliance is holding talks with administrators of Greensill Capital, which filed for insolvency this week, on a standstill agreement, GFG’s head Sanjeev Gupta said on Friday. “We are also having constructive discussions with Greensill’s administrators ... negotiating a formal standstill agreement,” Gupta said in an internal message to GFG workers made available to Reuters by the company. (Reporting by Eric Onstad; Editing by Edmund Blair)