The 29-year-old has prevously played at lock for the Celtic Warriors.

The region, looking to bounce back from the opening Heineken Cup defeat against Toulon, name an unchanged backline for the must-win clash tomorrow night.

Ospreys director of coaching Scott Johnson said: “The reasons behind the selection are twofold.

“JT has started the year at eight as Ryan was unavailable for a period of time. He was asked to fill the void because of Ryan’s injury and in fairness to him he has done exceptionally well.

“Saying that, we’ve certainly missed Ryan’s contributions so we wanted him in the team. We feel that balancing that one change, rather than the two it would be if they swapped positions, is better for the team given the short turnaround and preparation time for the week.

“We needed Ryan’s effectiveness and his work-rate, the team needed that, but it’s too complicated to start moving everyone around. We are very happy with JT, and Ryan was happy to do that for the team.

“To put Ryan at eight and move JT to lock, it changes everything, calls, line-outs, and we didn’t want to go down that path for a five-day turnaround. We think that Ryan has had enough game time now to warrant his place at the start. If we had two weeks then maybe we would do it differently, but we haven’t, so for the sake of not having to change everything, we’ve gone with it this way.”

The duo were advised of the decision simultaneously, along with the reasoning behind it, and Johnson says the response was exactly as he anticipated it would be:

“Ryan is a great team man, he has no issue at all with doing this for the team, which is exactly the kind of response we expected from him. They were both told the situation at the same time, we explained the logic to them and there were no issues.

“I promised JT at the start of the season that once a bloke gets the shirt, it’s up to the others to get it off him, and we are supporting his form as a coaching team. At the same time, we are acknowledging the work that Ryan has done, and the work that we’ve missed.

“Ryan has played there before, and I genuinely believe that after the World Cup we’ll probably see a bit more of him there. He’s such a brave and industrious player, the way the game is going he will give us a competitive edge, and we wanted as many good athletes out on the pitch as we can.”

Forwards coach Jonathan Humphreys said: “Obviously, we were disappointed to lose out in Toulon, particularly having managed to work ourselves into a good position with just a few minutes left. That’s the Heineken Cup for you though isn’t, the quality of the opposition, particularly in this pool, means that you can’t give them an inch or you will pay the price.

“We haven’t dwelt on it, with a short turnaround to a Friday night game there isn’t time to. We know that we face another particularly tough challenge in the shape of London Irish, a quality side who have had a great start to the season, top of their domestic league and securing the win against Munster on Saturday night.

“This is a pool that will go down to the wire, make no mistake about it. We were sat in the airport last week following the scores and even though London Irish were pulling away we all felt Munster would get a bonus point, which is how it turned out. It’s very evenly poised at the moment, the two homes teams have won without picking up a bonus, the two away teams have got bonus points. It’s no different than anyone anticipated and it’s exciting to be involved in it."

Ospreys team to face London Irish:

15 Lee Byrne, 14 Tommy Bowe, 13 Andrew Bishop, 12 James Hook, 11 Shane Williams, 10 Dan Biggar, 9 Mike Phillips, 1 Paul James, 2 Richard Hibbard, 3 Adam Jones, 4 Ryan Jones, 5 Alun Wyn Jones (Capt), 6 Jerry Collins, 7 Marty Holah, 8 Jonathan Thomas

Replacements

16 Huw Bennett, 17 Ryan Bevington, 18 Craig Mitchell, 19 Ian Gough, 20 Justin Tipuric, 21 Jamie Nutbrown, 22 Gareth Owen, 23 Nikki Walker