The imposing figure of Paul O'Connell will cast a large shadow over Welsh hopes of a triple crown and a possible grand slam with the Munster lock having proved his fitness to start his first international on Saturday since his country's ill-fated World Cup campaign. However, while that was the good news for Eddie O'Sullivan, the Ireland head coach is having to wait to see who will play at full back, with Geordan Murphy and Girvan Dempsey considered doubtful for the pivotal RBS Six Nations Championship game in Dublin, where Wales have not won since 2000.

A bulging disc in his lower back sidelined O'Connell straight after the tournament in France last year. The injury did not need surgery, only a prolonged period of rest that served to add to the talismanic forward's sense of frustration. A first attempted comeback in January failed and he resumed playing only last month, initially for Munster's second team, then for a half for the province in the Magners League against Edinburgh. That, though, was enough for O'Sullivan to fast-track him back against Scotland as a replacement. His appearance after an hour was warmly received at Croke Park and his arrival and that of Rory Best, the hooker, who also starts - they are the two changes to the side - brought immediate order to what had been a chaotic Ireland lineout.

O'Connell, who has 50 caps, admits he is a little rusty. “I could have done with another 80 minutes but I have got good natural fitness,” he said. “I had to take things week by week. With a back injury I couldn't do weights or speed work. All you can do is sit and relax and try to let it get better. It was so frustrating not having a timeframe.”

Losing two full backs is another scenario confronting O'Sullivan, who will wait until tomorrow to assess his options. Murphy has a slight Achilles strain connected with the operation he had on his broken leg five years ago and took no part in training yesterday. He aggravated the injury in Leicester's Guinness Premiership win over Leeds Carnegie at the weekend.

Dempsey, who missed the win over Scotland in which Murphy turned in a man-of-the-match performance having been dropped only three days before, is still nursing a hip injury. He at least trained but the head coach rates their chances of making it as “nip and tuck”. If each is ruled out, as O'Sullivan seemed to indicate they would be, then Rob Kearney would revert to his favoured position at No15, with Shane Horgan coming in on the right wing and the in-form Tommy Bowe switching to the left. Luke Fitzgerald would then come on to the bench for Horgan.

If either does make it then O'Sullivan's decision is made for him. If both report for duty then Dempsey would be favoured to regain his place. “This [game] is the biggest challenge of the championship,” O'Sullivan said. “Wales have momentum after three consecutive wins. The last time we saw them playing with such confidence was in 2005 when they won the grand slam. It is a pivotal game which will have a real bearing on the outcome of the championship.”

Croke Park teams

Ireland: G Dempsey (Leinster) or G Murphy (Leicester); T Bowe (Ulster), B O'Driscoll (Leinster, captain), A Trimble (Ulster), R Kearney (Leinster); R O'Gara (Munster), E Reddan (London Wasps); M Horan (Munster), R Best (Ulster), J Hayes (Munster), D O'Callaghan (Munster), P O'Connell (Munster), D Leamy (Munster), D Wallace (Munster), J Heaslip (Leinster). Replacements: B Jackman (Leinster), T Buckley (Munster), M O'Driscoll (Munster), S Easterby (Llanelli Scarlets), P Stringer (Munster), PWallace (Ulster), S Horgan (Leinster).

Wales: L Byrne (Ospreys); M Jones (Llanelli Scarlets), T Shanklin (Cardiff Blues), G Henson (Ospreys), S Williams (Ospreys); S Jones (Llanelli Scarlets), M Phillips (Ospreys); G Jenkins (Cardiff Blues), H Bennett (Ospreys), Adam Jones (Ospreys), I Gough (Ospreys), Alun-Wyn Jones (Ospreys), J Thomas (Ospreys), M Williams (Cardiff Blues), R Jones (Ospreys, captain). Replacements: M Rees (Llanelli Scarlets), D Jones (Ospreys), I Evans (Ospreys), G Delve (Gloucester), D Peel (Llanelli Scarlets), J Hook (Ospreys), S Parker (Ospreys).