The 63-year-old said that he finds the actor attractive at the Carousel of Hope gala in Beverly Hills, California, in which Clooney was the guest of honour for his philanthropic work, reported Huffington Post online.
"What do you girls say when you like another girl, but you're straight? George could be my boy crush," Simmons said.
The singer's wife, Shannon Tweed, was also very complimentary about Clooney, praising his giving nature.
"You can't even fault anything about George. As much as you wanna criticise movie stars for what they make and do, he gives," she added.
Clooney also appeared at the event, which raised USD 2.5 million to benefit the Barbara Davis Center for Childhood Diabetes and joined singer Neil Diamond on stage to sing his classic track 'Sweet Caroline'.