Jimmy O'Brien has joined fellow Ireland wing Mack Hansen in being ruled out of the Six Nations through injury.

Leinster revealed later on Monday that O'Brien has picked up a neck injury and will be unavailable "for a number of months".

The pair join Dave Kilcoyne in missing the Six Nations, with the prop out for six months with a shoulder injury.

Hansen is undergoing surgery on Monday for the injury which he sustained in his side's win over Munster in the United Rugby Championship on New Year's Day.

The Australia native has won 21 Ireland caps and played an important role in their Grand Slam success last year.

He also started three of Ireland's four group games at the 2023 World Cup as well as starting in their quarter-final defeat by New Zealand in Paris.

O'Brien, who has eight Ireland caps, came on as a replacement in the World Cup last-eight encounter.

The 27-year-old last played in Leinster's Investec Champions Cup win over Sale on 16 December.

Ireland begin their Six Nations defence against France in Marseille on 2 February.

Head coach Andy Farrell will next week name an extended squad for a training camp in Portugal ahead of the start of the 2024 competition.

"It's disappointing for us to lose Mack for such a period of time," Connacht head coach Pete Wilkins told RTE Sport.

"Obviously there'll be a knock-on effect to the Irish campaign in the Six Nations and most of all disappointment for Mack.

"He was starting to find some form and rhythm having been a little bit stop-start since the World Cup.

"Everyone loses out in that sense and the fans will miss watching him play as well so it's up to us to fill that gap and other players get a chance to step up.

"He's not lost his sense of humour, thankfully, he was in with us at the end of last week so very much around the place albeit in a sling.

"He's gone off for surgery today. We've had lots of contact with him. It's about trying to keep his spirits up. The key thing is to get this surgery and these initial couple of days out of the way and you can start on that rehab campaign.

"He's had a shoulder injury before, a similar injury when he was at Brumbies in Australia so although that's unfortunate to have it twice, at the same time he's familiar with the surgical process, familiar with rehab and that length of time."