The 33-year-old has been going behind the actor's back to have the age-defying injections, reported Showbizspy.
"For a while now, she's been sneaking around behind George Clooney's back and getting Botox treatments. Stacy doesn't want George to know because he hates plastic surgery on women.
"Stacy thinks she looks pretty good for someone in her thirties and says there are some things George doesn't need to know. Her Botox is one of them," a source said.
The couple have been dating each other since July this year.