ONE of the most controversial calls when Vern Cotter named his Rugby World Cup squad earlier in the week was that Josh Strauss, who is currently not qualified to represent the country, is among the 31. It is a decision based on trust with no concrete evidence that he can transfer his powerhouse play at club level to the international sphere.

By a twist of fate, this evening sees him coming up against one of the players discarded to make way for him. John Barclay played for Scotland at every age grade, won his debut cap in eight years ago in the 2007 World Cup and has gone on to win 40 caps for his country.

So there is a lot at stake for both the players and the coaches when the two take to the field in opposition back rows when the Scarlets – Barclay's current side – arrive at Scotstoun this evening as the home side launch their defence of the Guinness PRO12 title.

The problem for Strauss is that he will not complete his three-year residency period to become eligible to play for Scotland until later this month, so while the rest of the national side have been preparing on the international field he has not been allowed to play.

The solution has been to send him back to Glasgow Warriors to play, and Gregor Townsend, the head coach, has been delighted to see him. "It is another game for him to get more match fitness," Townsend said. "He is unavailable to play for Scotland until the World Cup starts.

"He played 80 minutes for us last week against Canada and in the second half he showed his fitness with a lot of ball carries and a lot of work defensively. Both him and the Scotland coaches – I would imagine – are happy that he can get two games under his belt so his match fitness is at a high level for the bigger challenges that lie ahead.

"I believe he will be an excellent Test player. He has played very well for us and was outstanding in the [PRO12] final against Munster. The international environment is different, a higher level than PRO12 and Champions Cup, but Josh has all the attributes to do very well for Scotland."

The problem for Cotter is that he won't get the chance to see what Strauss can do for Scotland until the first game of the World Cup, at the earliest – though last week's clash with Canada and this week's against a highly rated Scarlets back row including Barclay, gives him a strong hint.

"It happens a lot that players are moving between squads," noted Townsend. "They come back in and pick things really quickly. With Josh it helped that we went to Canada last week. He joined up with us on the Sunday before, we had an in-house game then we left for Canada so there were no distractions."

Townsend has had to work out how to open the PRO12 defence with 19 players away on World Cup duty, with Strauss due to make it 20 when he heads back to the Scotland camp next week. Despite that, he is confident that they have enough strength in depth to weather the storm.

"We have got a lot of quality players here," said Townsend. "It was great getting guys back from the Scotland, it helped with the competition and depth but we felt right from the pre-season that we have a lot of very good players who have trained very well."

Townsend has included all the players who failed to make Scotland's final 31 and has also included one of the leat experienced locks in the squad in Scott Cummings, the 18-year-old who showed up well in both the pre-season matches.

Glasgow: G Bryce; L Jones, P Murchie (Captain), F Lyle, R Hughes; S Wight, G Hart; J Yanuyanutawa, P MacArthur, M Cusack, R Harley, S Cummings, J Strauss, C Fusaro, A Ashe. Replacements: K Bryce, A Allan, Z Fagerson, K Low, T Holmes, M Blair, R Clegg, R Fergusson.

Scarlets: S Evans; H Parkes (C), R King, G Owen, M Tagicakibau; D Jones, A Davies; P John, E Phillips, P Edwards, T Price, L Rawlins, A Shingler, J Davies, J Barclay. Replacements: K Myhill, R Evans, W Taylor, G Earle, R Pitman, R Williams, A Thomas, T Williams.

Referee: Gary Conway (Ireland).