Clooney said while he thought Clinton was qualified for the job, the way she ran her campaign infuriated him.
"It was frustrating because I never saw her elevate her game," Clooney told the Daily Beast."I never saw it."
Even his liberal friends, he said, weren't impressed.
"I had a lot of liberal friends who were like: 'She not good at this,'" the Oscar-winning actor and director told the Beast. "And I see that, and I understand it."
He said her speeches "didn't soar." But Clooney also suggested that her gender was the reason her presidential aspirations sputtered.
"I think the fact that she's a woman made it a much harder uphill battle," he said.
Clooney and his wife, human rights lawyer Amal Clooney, hosted a fundraiser for Clinton during her presidential campaign where tickets fetched from $33,400 to $353,400. Supporters of her primary challenger, Sen. Bernie Sanders, showed up to protest the event.
He later acknowledged on NBC's Meet the Press that the ticket prices were "obscene."