American MMA fighter Holly Holm backed Conor McGregor to cause Floyd Mayweather problems on Thursday after their cross-over boxing showdown was confirmed.

Ireland’s McGregor will be the heavy underdog against 49-0 Mayweather but Holm knows a few things about upsets, after she ended Ronda Rousey’s unbeaten run with a brutal knockout in 2015.

“I’m one of those who believes in being able to cross over,” said Holm, a former boxing world champion, ahead of her UFC fight in Singapore on Saturday.

“Boxing is a whole different world... but Conor really believes in himself, and I think he’s going to put up a good fight.” Mayweather and McGregor – kingpins of their sports – will face each other over 12 rounds at Las Vegas’s T-Mobile Arena on August 26.

Neither has fought this year. Mayweather, 40, retired from pro boxing in 2015 after defeating Andre Berto, while McGregor (21-3) beat Eddie Alvarez last November.

Mayweather is the strong favourite but Holm, who will face Brazil’s Bethe Correia in Singapore, said fights can be unpredictable. “Anything can happen so that’s why I like to watch from the outside, it’s unknown, you don’t know what’s going to happen,” the American said.

Li Jingliang, a leading Chinese MMA prospect who is also on Saturday’s card, said McGregor had the tools to upset Mayweather.

“It’s a very good opportunity to show an MMA fighter is a well-rounded fighter, they can win in MMA fights, and also in boxing,” Li said through a translator. “I’ve been watching him, Conor has a reach advantage and he’s more powerful.”

Joe Carr, head of international and content at UFC – the organisation that made McGregor a star – also tipped the Irishman to cause an upset.

“The difference in combat sport is that one punch can change everything and what you need to do is to land that one punch. “What we know is that Conor McGregor is a huge hitter and he’s been knocking people out for the last few years,” Carr said.