Wallabies coach Ewen McKenzie says Nathan Charles defies ‘science and logic’ after setting up a Test debut for the cystic fibrosis sufferer.

Wallabies coach Ewen McKenzie has hailed cystic fibrosis sufferer Nathan Charles as a medical marvel after lining up a Test debut for the inspirational Western Force hooker.

Dumped Wallabies skipper James Horwill loomed as the feel good story for Saturday night’s second Test against France in Melbourne after game-one injuries paved the way for him to celebrate his 50th match for Australia back in the starting line-up.

Horwill is in the run-on side for lock Sam Carter (ankle), NSW Waratahs hooker Tatafu Polota-Nau replaces Stephen Moore (knee) and Western Force workhorse Ben McCalman slots in at No.8 for Wycliff Palu (ankle).

However, McKenzie admitted Charles’s tale was hard to beat – and explain.

Charles, believed to be the only cystic fibrosis sufferer in the world who has a professional career in a contact sport, is in line for a Test debut along with Melbourne Rebels pair Laurie Weeks and Luke Jones after their selection on the bench.

Charles, 25, requires up to 28 pills and vitamins every day to manage his condition – not that McKenzie could tell.

“I was talking to the doctor today – he (Charles) seems to defy science and logic,” McKenzie said.

“I think if anyone had not said anything to us, we would not have known (about his condition).

“I always talk about journeys, how people get there and he’s got a very unique story.

“I am glad it is out in the open and I think the best we can do to acknowledge him is to give him an opportunity on the field.”

While impressed by Charles’s triumph against the odds, McKenzie said the Force hooker had leapfrogged the more-established James Hanson in the Wallabies’ queue on his own merits.

“He handles the medical side of it himself. There is nothing I notice or see – he just functions like everyone else,” he said.

“We’ve had people on the bus with diabetes and all sorts of things. They learn to function and find a way.

“They do what they need to do – I don’t get involved.

“I just deal with them as a footballer and he (Charles) has been a really good addition to the squad.”

Milestone man Horwill’s injection into the starting line-up also brought a smile to McKenzie’s face.

“I’ve seen the many contributions he’s made to rugby in this country over a long period and I couldn’t be more pleased to be part of his milestone game,” he said.

Horwill is finally savouring some good fortune after being replaced as skipper by Ben Mowen during last year’s spring tour before Moore took over the reins.

Adding further insult, Horwill had been overtaken in the Wallabies’ second-row pecking order by Carter and Rob Simmons.

“It has probably taken me a bit longer and injuries play a part in that,” Horwill said of his milestone.

“The important thing now is to get the result and sew up the series.”

Palu – injured in last weekend’s 50-23 first Test win in Brisbane – is set to return for game three in Sydney.