Credit Suisse Group AG may need to find new ways to serve clients who generate as much as $750 million of revenue at its U.K. subsidiaries after Britain leaves the European Union, Chief Financial Officer David Mathers said. Losing access to European markets would endanger 10 percent to 15 percent of income at the two units, which have a revenue base of $4 billion to $5 billion, Mathers said in an interview this week in Zurich.