Former Ireland international and three-time British and Irish Lion does Ronan O’Gara does not believe that Johnny Sexton and Owen Farrell can start together for this year’s crop of Lions.

Much has been made of the battle between Sexton and Farrell to claim the number 10 jersey for the Lions in their first test against New Zealand on June 24.

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The suggestion that both players could start against the All Blacks is gaining traction, with the prospect of Farrell playing at 12 and Sexton at 10, something with head coach Warren Gatland has mentioned previously.

Farrell has played alongside George Ford in the number 12 shirt for England, but that duo have played alongside each other since school and have the kind of understanding that takes more than a month to build.

O’Gara is open to the prospect of having both Sexton and Farrell on the same pitch, but believes that it should only come in the closing stages of a Test.

Speaking to RTÉ 2fm’s Game On, he said. "I think you can definitely play them [together] I would like to think you’d play them after 50 minutes though. I don’t think it’s a good idea starting the two of them.

"Maybe against nine out of the other ten nations in the world you could but I just think with Sonny Bill Williams and Savea and their physical presence you can’t.

"They [Sexton and Farrell] are two 10s, they’re two really good ball players and there’s very little between the two of them.

"Farrell probably shades it in the fact that he’s had such an exceptional year with England and Saracens, but there wouldn’t be much between them.

"The issue is that it’s very hard to name a stand out midfielder for the Lions. Who’s going to play 10, 12, 13? If you ask anyone you get three different answers."

For O’Gara the issue is further complicated by the quality of the opposition that the Lions are facing.

The Racing 92 coach believes that the Lions are facing the best team in world rugby and that a Test win for the visitors would be a huge achievement.

"It’s winnable if you get unbelievably excited by the opportunity and I think that opportunity is, well let’s be realistic, it would be biggest achievement in rugby in an awful long time.

"It’s not the same as going to Australia, it’s not the same as going to South Africa, that’s achievable," he added.

"I think this is really, really difficult but I think certain players will grow with that pressure and other players will crumble.

"There should be massive excitement about the opportunity to create history. There should be certain players there who are capable of driving it, but it’s the hardest thing in rugby to do."

Ronan O'Gara was in Ireland to launch the SoftCo Foundation in Dun Laoghaire Golf Club where more than €150,000 was raised for charity and a further €100,000 committed for ongoing Cancer Research. The Foundation has selected three charities to partner with for 2017; CMRF Crumlin, the Irish Injured Jockeys Fund and Guys Cancer, London.