Ireland will have to endure an anxious 24 hours or more before they know the extent of the hamstring and groin injuries that afflicted their dynamic, game-breaking midfield pair of Brian O'Driscoll and Gordon D'Arcy in yesterday's 19-9, opening Six Nations win in Cardiff.

Coming on top of Shane Horgan's absence from the first two or three games with a knee injury, what has been a source of strength unrivalled by any other midfield in the world is suddenly in danger of looking skeletal

D'Arcy picked up his groin problem in the opening salvos, receiving treatment as early as the fourth minute, which made his ball-carrying tour de force and man-of-the-match performance all the more remarkable. He was compelled to see out the full 90-plus minutes, in part because O'Driscoll had received lengthy treatment for his hamstring problem in the 58th minute.

"He's gone straight into rehab, as every minute counts, especially with such a tight turnaround," commented Irish coach Eddie O'Sullivan in reference to his captain's absence from the post-match press conference and next Sunday's historic meeting with France at Croke Park. "He felt a twinge and we'll learn more tomorrow."

O'Sullivan was more optimistic about D'Arcy's chances, speculating that the centre's ability to complete the match was a good sign. Comparing them to thoroughbred racehorses, he admitted two such dynamic centres are unfortunately prone to such injuries.

When pushed, though, O'Sullivan conceded: "I suppose Gordon D'Arcy will be okay but Brian is definitely a doubt."

Were O'Driscoll to cruelly miss out on such a momentous day, Ireland would probably start with the back line that finished in the Millennium Stadium yesterday, namely with Andrew Trimble in midfield alongside D'Arcy and Geordan Murphy on the wing.

Were D'Arcy also to be sidelined, then the options are less plentiful, and O'Sullivan might be inclined to play Murphy alongside Trimble in midfield, with Tommy Bowe on the wing, rather than start either of the inexperienced Irish A pairing of Kieran Lewis and Barry Murphy.

All of this has uncanny and distinctly uncomfortable echoes of two years ago, when Ireland were also being hotly tipped to win the Six Nations or Grand Slam but saw D'Arcy and O'Driscoll both injured in the opening win in Rome. As it happened, neither was ruled out until the day before the second game in Scotland, even though both were having cryotherapy in the Spala ice chambers in Poland. Pack power and a Kevin Maggs-Shane Horgan midfield saw Ireland through in Murrayfield, and O'Driscoll made a try-scoring return at home to England in round three. But D'Arcy - player of the championship the year before - wasn't seen again in that 2005 Six Nations.

Either way, the loss of O'Driscoll and/or D'Arcy would be a potentially crippling blow to Ireland's title/Slam ambitions.

Admittedly, those ambitions looked a bit fanciful during stretches of yesterday's win, especially during a first half spent largely on the back foot. Gifted a try after 48 seconds, and stealthily breaking upfield during an inspirational nine-minute cameo by Murphy in place of a bloodied Denis Hickie for O'Driscoll to score, Ireland somehow led 12-9 at the break.

A 71st-minute try by Ronan O'Gara, which he converted from the touchline, closed out a nervous win.

O'Sullivan bridled a little at the notion that a similar performance would not suffice against France, though he accepted such an assessment was "probably true", and admitted that Ireland's tactical kicking, work at the breakdown and protection of the ball were not of the requisite quality.

"You have to balance that up with our defensive performance, especially off turnovers, and scoring three tries," he argued. Speculating that it was the type of game Ireland might have lost a couple of years ago, he added: "When the chips were down we didn't panic and we killed the game off, so there were positives and negatives."

His counterpart, Gareth Jenkins, looked like he had been mugged and spoke like he had too. "They're a wise old bunch," he said of an Irish team that, significantly, boasted over 18 caps per man more. "They controlled that game without the ball for a lot of the time. They are a very streetwise side and they got three tries out of that game, and you have to ask from where and how did they get them?

"This is their uncanny strength and this is where they showed their experience really."

The Irish scrum stood up well, as it invariably does when most under the microscope. Defensively, limiting Wales to just three penalties was a near Herculean effort, mentally they toughed it out and there were some excellent individual performances in the midst of such a harrowing opening-day win.

Battling through the pain barrier, D'Arcy gave one of his water-into-wine performances; Ronan O'Gara came through when it mattered; Denis Leamy was utterly immense in defence, at ruck time and in open field; while Simon Easterby - an utter nuisance to the Welsh in more than justifying his selection - and David Wallace weren't far behind.

That said, O'Sullivan might well give some thought to recalling the physicality of Neil Best to counter Sebastien Chabal and co when announcing his hand on Wednesday. For all his pre-tournament talk of rotating his 40-man squad, French coach Bernard Laporte has made only two enforced changes from the 22 who were on duty in their 39-3 win over Italy in Rome on Saturday. Sale hooker Sebastien Bruno and Perpignan centre David Marty replace the injured duo of Dimitri Szarzewski and Toulouse's Florian Fritz, underlining the impression Laporte will want to see Chabal and the new halfback pairing of Pierre Mignoni and David Skrela in tandem again in a largely unchanged side.

For all Italy's supposed strength up front, from the first maul and the first scrum the French pack were on top, and Chabal's power and ball-carrying, along with the presence of a proper outhalf, gave them a shape and direction lacking last autumn. O'Sullivan admitted Ireland cannot afford to give France that kind of momentum.

In tandem with England's Jonny-inspired rejuvenation on Saturday, suddenly the scale of the challenge facing Ireland over the next two weekends looks more daunting, and, against France, more in keeping with opponents who have won their last four meetings with Ireland.

The heavyweights are back, and Ireland need the dancing feet of their first-choice midfield.