By Simon Jessop and George Georgiopoulos LONDON/ATHENS (Reuters) - As Greeks, fearful their country is heading for a default, withdraw billions of euros from banks, those lenders are fighting to limit the fallout by steering clients towards investment funds. On Friday, 1.2 billion euros (£0.86 billion) was withdrawn from the banking system, sources said, to take this week's outflows to around 4.2 billion euros. While the head of the Greek central bank has said the system is stable, the European Central Bank said it did not know if Greek banks would be able to open on Monday.