Michael Cheika and Mario Ledesma© Laurence Griffiths/Getty Images

Michael Cheika has praised Mario Ledesma's contribution to the Wallabies' World Cup campaign, saying the Argentine has not only worked wonders with the scrum but also understands how to get to the "heart" of the players.

Ledesma's twin loyalties have put him in the spotlight ahead of the Rugby World Cup semifinals, with the former Pumas hooker now part of an Australian coaching staff preparing for a showdown with the nation he represented with great distinction throughout his 15-year, 84-Test career.

Having joined Cheika's staff in July, Ledesma has transferred his scrum expertise to the Wallabies to such effect that they enjoyed dominant set-piece performances against Wales and England, before a tough outing against Scotland in Sunday's quarterfinal.

But his contribution extends well beyond the set piece, according to Cheika. The head coach lauded the 42-year-old's all-round skill-set that has helped guide the Wallabies within one win of a fourth Rugby World Cup final.

"Obviously he's been brought in to deal with the set piece, predominantly from a coaching point of view," Cheika said on Friday. "One of the big reasons it was easy to bring Mario in was also that he's got a very good way of expressing himself in English as well.

"Having coached in foreign countries, in foreign languages, it's one thing talking the language but it's another thing actually making the point in a rugby sense, where sometimes you need to get to the heart of the player and where the language isn't always the natural translation.

"Mario has been able to conquer that in his early days in Australia and been able to get to the heart of the players, to link the technical with the mental and the passion side as well. And it's always about balancing that and being very clear on what the outcomes are. So I think he's done really well in that way."

Just eight years ago Ledesma was part of a Pumas side that achieved its best ever World Cup result -- a third-place finish at France 2007.

He could therefore have cause to feel a little uneasy this week as he seeks to deny them a maiden final appearance, but Cheika said there had been no obvious change in the Argentine's demeanour.

"He's not playing, so it's not that special you know what I mean, in that regard," Cheika said. "He had his chance to play, for about 50 years I think he played for, so he's had plenty of games.

"He'd probably like to," Cheika joked, "but I think he injured his calf playing touch football with the staff. So he's probably out.

"It's an interesting match obviously because we're against his country, his nation of birth, who he's played passionately for. Me, personally, I see that as a great challenge; when you play against your old team or you go into battle against those guys that you've been with for many years, I think it inspires you to want to do better.

"And I think that for someone like Mario it's going to do exactly the same thing. I think this is probably something that will motivate him to want to do better than he's ever done before."