EVERY year, the handful of games that clash with the RBS Six Nations Championship are make or break time for all the top clubs when it comes to league ambitions. This year, the stakes in Scotland are as high as they have ever been with both Glasgow Warriors and Edinburgh knowing they have to pull out results despite their missing Test players or they could get knocked out of the play-off race.

To make life even tougher, they both open their Six Nations period away against the teams who went into this weekend's round of matches in the Guinness PRO12 occupying the top two places – Glasgow travel to Ulster, who got to experience life at the top of the table when they won their catch-up game in Newport last week. Edinburgh, meanwhile, are en route to face the Scarlets, a point behind.

Between them they have 17 players away with the national squad – one of the issues with the PRO12 is that while having nearly 50 players starting for their national teams is great for competition for the rest of the season, it does hurt the quality while they are away – and that puts huge pressure on the back-up players to perform.

For Glasgow, who have a number of injuries as well, that means a first start for Gregor Hunter, the fly-half they acquired last season from Edinburgh but who has had to come through a serious knee injury before he could start playing again.

“He has worked really hard in training this season and has been playing regularly for Glasgow Hawks, so we're expecting him to play well in a Warriors shirt," commented Gregor Townsend, the head coach.

The team arrive in the game after drawing against the Ospreys a fortnight ago, a match that highlighted the season's failing of playing well for most of the match, but not being able to sustain the level of performance all the way through: "We played well against Ospreys for around 60-65 minutes, but we’ll need an 80-minute performance to come away with a positive result. I’m looking forward to seeing this group of players front up in a big game for the club," he said.

Edinburgh, meantime, have had to recall Blair Kinghorn and Jamie Ritchie from the Under 20s squad, but can at least hold out hope of an end to their lock injury crisis with both Ben Toolis and Anton Bresler returning to action in a side that shows five changes from the team that lost in Cardiff in their last outing.

Scarlets: M Collins; G Owen, R King, H Parkes (C), DTH van der Merwe; S Shingler, R Williams; P John, K Myhill, P Edwards, G Earle, D Bulbring, A Shingler, W Boyde, M Allen. Replacements: R Elias, D Evans, R Jones, R Pitman, S Hughes, A Davies, A Thomas, S Evans.

Edinburgh: G Tonks; D Hoyland, M Allan, S Beard, T Brown; P Burleigh, N Fowles; R Sutherland, N Cochrane, J Andress, A Bresler, B Toolis, M Coman (C), H Watson, C Du Preez. Repalcements: G Turner, A Dell, S Berghan, A Toolis, J Ritchie, S Kennedy, B Kinghorn, D Fife.

Referee: A Brace (Ireland)

Ulster: S Olding; C Gilroy, D Cave, S McCloskey, J Stockdale; S Windsor, R Pienaar; C Black, R Herring (C), R Lutton, A O'Connor, F van der Merwe, R Diack, S Reidy, N Williams. Replacements: J Andrew, K McCall, B Ross, C Henry, R Wilson, P Marshall, P Jackson, S Arnold.

Glasgow Warriors: P Murchie; L Jones, G Bryce, S Johnson, R Hughes; G Hunter, A Price; R Grant, P MacArthur, S Puafisi, G Peterson, L Nakarawa, R Harley, S Favaro, R Wilson (C). Replacement: J Malcolm, A Allan, D Rae, J Strauss, C Fusaro, G Hart, P Horne, T Naiyaravoro.

Referee: M Mitrea (Italy)