Sean McMahon expected to be spending the next week living it up with his Melbourne Rebels teammates in Mexico, reflecting on a rugby season he already considered a fairy tale.

Instead the 20-year-old backrower will likely be preparing to make his Test debut against Wales, after seizing an unexpected opportunity against the Barbarians.

McMahon had to wait only 19 minutes to make his Wallabies debut off the bench in Saturday’s 40-36 win over the Barbarians at Twickenham after veteran Scott Higginbotham was forced off with a hamstring injury.

He made the most of it with a barnstorming display which featured a try and coach Michael Cheika said he was in the frame for selection in the squad for Saturday’s Test at Cardiff’s Millennium Stadium.

“I thought he was outstanding,” Cheika said of McMahon.

“With the injury to Scott Higginbotham there’s a place in the backrow open for the Test next week and he’s definitely put himself right up there.”

McMahon only found out about his surprise selection for the spring tour squad two days before he was due to fly out on an end-of-season trip.

He may not have been in the squad had a knee injury not ruled out Brumbies flanker Scott Vardy but few could argue McMahon deserved a chance after a maiden professional season that yielded three awards at the John Eales Medal, including the Super Rugby rookie of the year.

McMahon excelled with the Rebels, National Rugby Championship side Melbourne Rising, the Australian under 20s side – which he captained – and won Commonwealth Games bronze with the Australian sevens side in Glasgow.

The Brisbane-born forward isn’t counting his chickens when it comes to winning a spot on the bench against Wales but he can’t quite believe how things are panning out.

“I’m still in a bit of a dream at the moment. I’m pinching myself every day,” McMahon said of his 2014.

“(This tour) was definitely about the experience but as every Australian wants to do, you want to get that first Test cap and I was hoping for an opportunity and I’m going to just keep working towards that.”

McMahon’s readiness for the biggest stage isn’t surprising given he comes from a family of tough men.

His father Pat is a security expert primarily based in Gabon, west Africa, one of his brothers is a national security manager and the other a bouncer.

His family wasn’t planning to join him during the European tour but he McMahon says that could change if he earns Test selection.

McMahon’s rise comes despite Australia’s backrow depth and he feels lucky to be able to look up to the likes of Wallabies captain Michael Hooper, Higginbotham, Ben McCalman, Matt Hodgson and the injured David Pocock.

“Having them there and being able to play and train alongside them, that’s only going to build me up and help me be the best I can be,” McMahon said.

As for Mexico, McMahon hopes to get there one day after obtaining a full refund for his trip.

Higginbotham’s hamstring injury will be assessed in the coming days but there are fears his spring tour could be over.