Donncha O'Callaghan's availability for Ireland's next RBS Six Nations Championship game against England at Twickenham on Saturday week remains in serious doubt, though the extent of the medial knee ligament damage he sustained in Sunday's 36-15 win over Wales will not be known until today.

The Irish lock, who was forced off the pitch after 36 minutes of his first championship start, went for a scan yesterday but the results will not be known until today.

According to the IRFU press officer, John Redmond, "Donncha went back to Cork on crutches today but that was not necessarily an indicator as to his well-being, and was more for comfort. He was due to have a scan and although it looks as if he's certainly in a race against time he hasn't been definitively ruled out of the England game."

The prognosis on Gordon D'Arcy looks a good deal healthier, with Redmond confirming the initial post-match view that the Irish centre's bruised back should not rule him out of consideration for the game against the World Champions and reigning Grand Slam holders.

Were O'Callaghan to be ruled out, the options facing coach Eddie O'Sullivan would not be plentiful, given Leo Cullen is still sidelined. The most obvious call-up would be Gary Longwell given the Ulster man was amongst Ireland's four locks at the World Cup. Longwell, however, was dropped by Ulster coach Alan Solomons for their Celtic Cup final triumph over Edinburgh as well as their back-to-back meetings with Leicester in the Heineken Cup before regaining his place in the matches against Stade Francais and the Gwent Dragons. He has also played in Ulster's two most recent Celtic League matches.

Based on form at the top end of the European Cup, Trevor Brennan would undoubtedly have his claims, as well as his supporters, bearing in mind the Toulouse player held down a place in the second row for the European Champions throughout their four-match winning streak in January.

Others who might come into the reckoning include the New Zealand-born but naturalised Leinster lock Ben Gissing, while alternatively O'Sullivan could go with five backrowers in his squad and nominate Simon Easterby as second row cover; as he did for the final World Cup warm-up game against Scotland when Easterby played the last five minutes at lock.