Patti Stanger schooled Stacy Keibler on sealing the deal with her love of 10 months, George Clooney!

The Millionaire Matchmaker, 51, took Keibler aside at the Simon G. Jewelry Summer Soiree in Las Vegas June 2.

"She gave Stacy a big tip," an eyewitness tells Us Weekly. "She said that George needs to propose within a year of them being together."

PHOTOS: George's girls

If he doesn't?

The couple "won't have as strong a chance," the onlooker shares of Stanger's explanation.

PHOTOS: George and his ex Elisabetta in happier times

Despite Stanger's word of caution, the blonde beauty and the Descendants actor, 51, still seem to be going strong; the pair are currently vacationing at Clooney's famed villa on Italy's Lake Como.

Last December, the actor opened up to Esquire about his rep as Hollywood's ultimate bachelor.

PHOTOS: Clooney before he was a superstar

"I don't talk about [marriage] because I don't think about it. I don't ever question other peoples' versions of how they live their lives or what they do," Clooney told the mag, adding that "People forget that I was married. I love that." (He wed Talia Balsam in 1989; the pair split four years later).

Continued the Ides of March star, "Everybody sort of has their own versions of what they think I am and what they think that is . . . I'm just living my life and doing the best I can."

This article originally appeared on Patti Stanger Gave Stacy Keibler Relationship Advice!