Eddie O'Sullivan says that Ireland head coach Andy Farrell faces a crucial call at inside centre for Saturday’s Six Nations opener against Wales.

With Robbie Henshaw still sidelined with a wrist injury, Farrell’s options at 12 are Bundee Aki, Stuart McCloskey or the uncapped Jamie Osborne.

Aki is short on game time, having not been selected by Connacht since loss to Ulster on 23 December, while McCloskey has rediscovered some form in recent weeks as Ulster snapped their losing skid.

"It’s a tough one because effectively Aki hasn’t played for six weeks," former Ireland boss O’Sullivan told Against The Head.

"The options really are himself or McCloskey, they’re not going to pick Osborne. There’s a risk to it but it has happened before. Aki has come into the team with not much rugby under his belt and done okay.

"That to me is a crucial call, especially away from home. There’s not much room for error in Cardiff."

Johnny Sexton is expected to be fit for Saturday's game in Cardiff

Ireland have lost on their last four visits to Cardiff in the Six Nations but head into Saturday's game as the No 1-ranked side in the world and on a five-game winning streak that includes victories over New Zealand (twice), South Africa and Australia.

Ireland are strong favourites to get off their campaign off to a winning start but O’Sullivan is expecting a response from Wales now that his former colleague Warren Gatland is back at the helm.

"Cardiff is always a difficult place to win in the Six Nations," he said. "We know the Welsh teams don’t perform particularly well in the URC but put them into a Wales jersey and everything is different.

"It is one of the great mysteries of Welsh rugby, how they can elevate themselves when they put on that jersey, but they do, and every year you go to Cardiff it’s a tricky fixture.

"If you look at the fixture list, it often defines your Six Nations. For Ireland, definitely next weekend is crucial. If we win and then beat France, with all due respect to Italy and Scotland we’re looking at a Grand Slam game against England at home on the last weekend. That’s our trajectory.

"If we were to lose in Wales, suddenly you’re trying to scramble to rescue things. A win the first day out is crucial in the Six Nations, and then how your fixture list falls after that.

"The danger for us in Wales is Warren Gatland is back in there. He knows the runs of things, he’ll tighten the ship, pull things together.

"They have to react under Gatland and they will. That suddenly makes this game a lot trickier than if Wayne Pivac was still there, because we knew what we were getting there. This is a lot different."

Warren Gatland begins his second stint as Wales head coach against Ireland

Donal Lenihan is keen to see if Gatland will turn to the old guard who helped him win Grand Slams and reach Rugby World Cup semi-finals during his first stint as Wales head coach, or bring in young, in-form players such as back rows Jac Morgan and Tommy Reffell.

"I think Gatland will take a short-term view on this," said Lenihan. "He needs to get Wales organised for the World Cup. There’s a suggestion he’s in for five years but I think he will wait until the World Cup, see how they perform.

"There is a lot of good young talent and they will be dangerous, but it’s a massive task for him to try and swing it around in what is about two weeks’ preparation."

Follow every game of the Guinness Six Nations on RTÉ.ie/Sport and the RTÉ News app, or listen to live commentary on RTÉ Radio 1.

Watch live coverage of Ireland v France (11 February), Italy v Ireland (25 February) and Scotland v Ireland (12 March) on RTÉ2 and RTÉ Player.