Celtic League/Cardiff v Ulster:David Humphreys misses this match after picking up an adductor muscle injury in training this week. Paddy Wallace switches from centre to outhalf, with a fit-again Paul Steinmetz returning to partner Andrew Trimble in midfield.

Kevin Maggs is included among the replacements as is flanker Neil McMillan who returns to the Ulster squad for the first time since fracturing a thumb in January. Ulster, the defending Magners Celtic League champions, trail Leinster by five points and know victory is the only commodity that will sustain their title hopes.

Cardiff thumped Edinburgh last week and they are 11 points behind Leinster but with two games in hand. Coach Dai Young has made two changes from the last game. Jamie Robinson comes in at centre with Taufa'ao Filise coming in at prop. Tom Shanklin and Gary Powell drop to the bench.

The home side have won their last dozen league matches at the Arms Park, and not being beaten at the Arms Park by an Irish team in the league since Munster were the visitors in November, 2005.

Ulster must not alone compensate for the direction and composure that Humphreys brings to this team - Wallace is an able deputy - but discover some form in what promises to be a tough encounter. Their victory over the Borders last time out was a little flattering but there were snatches of what this team is capable of.

It'll be a pretty attritional contest up front and the visitors will have to negate the influence of Welsh international openside flanker Martyn Williams. Cardiff are blessed with power and pace in the backline and in fullback Ben Blair have a top goal kicker.

It's difficult to see Ulster winning on the strength of their recent form but knowing that their season rests on this it could be the catalyst for a big performance.

CARDIFF: B Blair; R Williams, J Robinson, M Stcherbina, C Czekaj; N Macleod, M Phillips; G Jenkins, T Ryhs Thomas, T Filise; B Davies, R Sidoli; A Powell, M Williams, X Rush. Replacements: G Powell, G Williams, D Jones, M Lewis, E Fairhurst, N Robinson, T Shanklin.

ULSTER: B Cunningham; T Bowe, A Trimble, P Steinmetz, A Maxwell; P Wallace, I Boss; B Young, R Best, S Best; R Caldwell, J Harrison; S Ferris, N Best, R Wilson. Replacements: P Shields, J Fitzpatrick, T Barker, N McMillan, K Campbell, K Maggs, P McKenzie.

Referee: D Changleng (Scotland).

Verdict: Cardiff to win.