UFC superfan Demi Lovato has warned Floyd Mayweather, Jr. not to be too cocky about his upcoming fight with Conor Mcgregor - because he can't prepare for "crazy".

Most boxing pundits believe UFC star McGregor hasn't got a chance against unretired Floyd - but Demi insists her pick could shock the world with a major fight night knock-out.

"Conor's crazy, and sometimes you can't beat crazy," Demi told TMZ.

The singer has become a huge UFC fan, training at Jay Glazer's Unbreakable Gym in Los Angeles with some of the top mixed martial arts fighters in the world, and she believes a Conor win on 26 August (17) would be a big deal for the sport she loves.

Demi recently teamed her passion for mixed martial arts with her love of fashion, by joining forces with Kate Hudson's athleisure brand Fabletics, and revealed fight classes are a great form of therapy.

"I feel the most confident when I'm in the gym," she told Us Weekly. "Whenever I'm training - whether it's boxing, kickboxing, Muay Thai, jiu-jitsu."

Demi's Fabletics capsule collection, which includes cute heart print leggings, graphic tank tops and slogan T-shirts, debuted in May (17), with more designs coming next month (Aug17).