Pumas the mystery team of the World Cup semi-finals

Australia's centre Matt Giteau (C) attends a team training session at the University of Bath on September 16, 2015, in Bath prior to the start of the Rugby World Cup 2015. AFP PHOTO / MARTIN BUREAU
Australian centre Matt Giteau at a Wallabies training session. MARTIN BUREAU

ARGENTINA has emerged as a World Cup wildcard with Australia admitting the unpredictability of its semi-finals opponent makes it a dangerous threat at Twickenham on Monday morning (AEST).

The Wallabies have been tough in their past three victories - over England 33-13, Wales 15-6 and Scotland in a 35-34 quarter-final thriller - while Argentina has found its way into the semis with wins over Tonga (45-16), Namibia (64-19) and last weekend upsetting Ireland 43-20.

The challenge facing coach Michael Cheika and his players will be adjusting from playing three northern hemisphere sides to the Pumas, who have shown a willingness to play open, attacking football to become the surprise packets of the World Cup.

The Pumas have have fronted up in this World Cup with some genuine danger men in their outside backs, especially winger Juan Imhoff, who scored two tries against Ireland.

"They're good up front, their back three are good, they're just good everywhere," said Matt Giteau.

"They have their own style and when they're confident like they are, they are very, very dangerous."

Australia desperately needs flanker David Pocock (calf) to join Michael Hooper and Scott Fardy to match the power and intensity of the Argentinean back row.

"They (Pocock and Hooper) are two very special players who have done so much for Australia over the years and I just love playing alongside them," Fardy said.

Pocock, prop Scott Sio (elbow) and Israel Folau (ankle) have all trained, but Cheika has not yet revealed his squad for the do-or-die semi-final