Sean O'Brien could easily have been a star of the World Cup but as the Ireland team depart from Dublin Airport this afternoon, the flanker finds himself on a familiar comeback trail. 

Just over two years ago the Leinster man, who will move over to London Irish in December, shone as the Lions drew a Test series in New Zealand.

However, the Carlow native struggled to get a run of games under his belt the following year and missed out on Ireland’s Grand Slam run and Leinster’s Champions Cup success.

Then, in November 2018, he broke his arm in the win over Argentina, agonisingly missing the 16-9 victory over New Zealand the following week.

He played four games in this year’s Six Nations, winning the last of his 56 caps against Wales, but struggled to find form amidst a disappointing campaign for the holders.

His World Cup hopes came to an end in May when Leinster confirmed that he would undergo hip surgery and delay his move to London, which had been announced last February.

Sean O'Brien at Croke Park last month

It was a significant blow for Ireland coming two months after flanker Dan Leavy was ruled out with a serious leg injury. 

"I’d love to be there but obviously that’s not the case," the 32-year-old told RTÉ Sport at the launch of the broadcaster's Rugby World Cup coverage event.

"I miss being around the lads at this time of year. The excitement of leaving and having those games behind you and looking forward to performing at the World Cup is huge.

"I know from speaking to a few of them during the week how excited they are.

"It’s a strange enough time because I’m nipping in and out of Leinster, doing my rehab in the mornings. I’m gone for the rest of the day and I’m not involved in meetings or anything really got to do with them."

RTÉ will show all of Ireland's World Cup games

Despite much of the pre-tournament talk focussing on probable quarter-final opponents, New Zealand or South Africa, O'Brien urged caution ahead Ireland’s opening game against Scotland on 22 September.

"Everyone is talking about a quarter-final but Scotland are so dangerous," he said.

"To have then first up is a huge test.

"I think we’ll see a few surprises in the starting team. I think Pete [O’Mahony] will start at 7, Jack [Conan at 6] and CJ [Stander at 8].

"The rest of the team picks itself but it’ll be an interesting battle and if we don’t hit the ground running it’s going to be a long [or short] World Cup."

O’Brien also provided an update on his rehab and his thoughts ahead of emigrating after 14 years with Leinster.

"[It’s going] really good, to be honest with you I haven’t had any complaints since I had the operation," he said. 

"I see the surgeon on Friday and hopefully I can start squatting and getting strong through my legs again and I start running in two weeks.

"I had a little bit of a trot this morning in the gym, I wasn’t meant to but I had no issues. I’m looking forward to running around properly again hopefully.

"I don’t go until 3 December. I do all my rehab here so I’ll land over there hopefully fit and do probably a six-week programme with them and play straight away if the hip is good.

"I’ve a couple of more months of work ahead of me but I’m looking forward to it.

"It is frustrating. I’ve often said rehab is one of the toughest things you can do. As a professional all you want to do is go out and play.

"You don’t want to be stuck in the gym, doing two or three hours of rehab a day.

"On the other hand you take the positives out of it. When you are sitting on a bike for an hour you have a lot of thoughts and it’s good for the mind, mentally to get through that work and know you can come out the right side of it.

"I’ve had a few conversations with [London Irish Director of Rugby and former Ireland head coach] Declan Kidney in the last while and he’s exactly the same as before. I’m really looking forward to it.

"They’ve got a good coaching set-up. They’ve brought in Brad Davis from the Ospreys and they’ve built a good squad with a lot of lads coming in after the World Cup.

"I suppose it’s going to be about getting us all together and that we unite fairly quickly and put London Irish back on the map over there."

Meanwhile, Heatstroke has killed two people in Japan, as nearly half a million homes remain without
electricity after a powerful typhoon battered Tokyo and the surrounding area.

Ireland are due to base themselves in the region for a week upon their arrival.

RTÉ Sport will televise 14 live matches from Rugby World Cup 2019, including all of Ireland's matches, the knockout stages and a daily highlights show. RTÉ Radio will broadcast all Ireland's matches and you can follow the tournament via RTÉ.ie/sport and the News Now app.