Soros Fund Management took part in Santander's 7.5-billion-euro share sale, completed over several hours last Thursday, with a 500-million-euro investment, the source said, speaking anonymously because the matter isn't public. An investment of that size would give Soros' fund a roughly 0.66 percent stake in the euro zone's biggest bank, according to calculations using Thomson Reuters data, although these do not take into account the new shares to be issued.