Celtic League/Ospreys v Ulster, Liberty Stadium, 7.10. On TV: BBC Wales: Ulster coach Mark McCall knows that there is no recourse to events at Murrayfield if his charges win in Swansea tonight.

The Celtic League will spend a year in Belfast. He is further bolstered by the fact that they could still squeak home even in defeat and in this respect there are a couple of permutations, concerning bonus points or simply a Leinster defeat.

Ulster's task is compounded by the loss of their captain Simon Best to a broken ankle but that could well act as a motivational aid for his team-mates. Australian international Justin Harrison, a huge success on and off the pitch since his arrival last summer, takes over the leadership duties.

Former Irish international Justin Fitzpatrick is a pretty tidy deputy. He comes in at loosehead prop with Bryan Young moving across the frontrow to tighthead, a position he occupied with some success in a couple of A internationals for Ireland this season.

A timely fillip is the fact that Stephen Ferris is available despite the fact that he'll go into hospital for a small operation on his ankle after the match. The young flanker was immense in the draw against Llanelli.

McCall has reasons to be positive, notably the character his team displayed in holding on for a draw the last day and also the performance of the fledgling centre partnership of Paddy Wallace and Andrew Trimble. The former brings a subtlety, clever angles of running and good distribution while Trimble proved a real handful for the Llanelli defence. The halfbacks David Humphreys and Isaac Boss represent another unit that Ulster hope will fire on the night. The pack will win possession and have enough abrasive characters not to be cowed by what will be a very physical challenge from the home side. The Ospreys, the defending champions, have a goal of their own, namely to pip Llanelli and finish as the second-ranked Welsh team for next season's European Cup draw. They need to win.

Coach Lyn Jones admitted: "We are delighted to have confirmed our qualification for next season's Heineken Cup. Although it's sad to reflect that it was just one year ago that we were experiencing the glory of winning the Celtic League at the Gnoll, there is a touch of irony that we now face an Ulster side coming to the Liberty Stadium looking to win the league.

"We are battling it out with the Scarlets to finish as the second-placed Welsh region. Ulster have chosen a side that signals their intent and we have done the same. Ulster were very unfortunate not to get a win at Stradey Park last weekend."

The Ospreys leave Stefan Terblanche and Matthew Jones on the bench and will be buoyed by the fact that they have won the last six games at tonight's venue and not lost at home to an Irish side since November 2004. Ulster have only beaten the Ospreys once in six meetings.

It's difficult to escape the fact that Ulster's need is probably greater and provided they cut down on the error rate and unearth a big performance up front it could be enough to squeak home.

OSPREYS: G Henson; J Vaughton, S Parker, A Bishop, S Williams; J Hook, J Spice; D Jones, B Williams (capt), A Jones; A Wyn Jones, I Evans; J Thomas, L Beach, A Lloyd. Replacements: R Hibbard, A Millward, P James, A Newman, R Pugh, M Jones, S Terblanche.

ULSTER: B Cunningham; T Bowe, A Trimble, P Wallace, A Maxwell; D Humphreys, I Boss; J Fitzpatrick, R Best, B Young; J Harrison (capt), M McCullough; N Best, S Ferris, R Wilson. Replacements: N Brady, R Moore, R Caldwell, N McMillan, K Campbell, J Bell, J Topping.

Referee: David Changleng (Scotland).

Leading points scorers: Ospreys - Gavin Henson 99. Ulster - David Humphreys 215.

Leading try scorers: Ospreys - Andrew Bishop 3. Ulster - Tommy Bowe 10.

Verdict: Ulster by a whisker.