When George Soros agreed last November to invest $500 million of his firm’s money with Bill Gross, the hedge fund billionaire gave the former “bond king” a vital endorsement in his first few weeks in a new job. It took less than a year for Soros to take it all back.

Soros Fund Management has pulled its entire investment from an account managed by Gross at Janus Capital Group because of poor returns, people familiar with the matter said.