“I do not believe the situation really is calm,” Gross, said on Monday in a Bloomberg Television interview, adding that he was surprised by the muted market reaction to a Greek vote on Sunday.

Financial markets barely shuddered after Greek voters emphatically backed Prime Minister Alexis Tsipras’s call for “no” to more austerity. The euro slipped less than 0.5 percent and U.S. stocks pared losses, in a sign investors see the crisis there as contained for now.

Greece needs to service marketable debt including 3.5 billion euros due on bonds held by the European Central Bank on July 20 and 3.2 billion euros a month later, Moody’s Investors Service said in an April report. Gross said the Greek standoff needs to be resolved quickly.

“I think they have a week or two to settle this,” he said, referring to a debt payment Greece has to make later this month. “You’re seeing massive support behind the scenes of course on the part of the ECB. You’re seeing central governments throwing everything they have at the markets and keeping them calm.”

Gross, who joined Janus in September after abruptly leaving Pacific Investment Management Co., now manages the $1.5 billion Janus Global Unconstrained Bond Fund. That fund gained 0.4 percent this year, trailing 64 percent of peers, according to data from Chicago-based Morningstar Inc.