Mack Hansen and Jimmy O'Brien are to miss the Six Nations, James Lowe is only just back in training and has not played since the World Cup, while Keith Earls and Andrew Conway have called time on their international careers.

It is safe to say Ireland could have a very different look to their back three as they seek to defend their Six Nations title, with Hugo Keenan the only winger or full-back from the World Cup squad currently on the pitch.

However, the misfortune of some will represent an opportunity for others.

BBC Sport takes a look at those who could benefit and force their way into Andy Farrell's plans.

Jacob Stockdale

There was an argument for Jacob Stockdale to be back in Ireland colours even before the injuries to Lowe, Hansen and O'Brien.

After bursting on to the scene with Ireland in 2017, the Ulsterman won a Six Nations Grand Slam the following year and has racked up an impressive 19 international tries. But injuries and a loss of form meant he dropped out of the Ireland picture.

We saw glimpses of his best form in the first half of 2023 and he has started the new season like a freight train, scoring six tries - to put it simply, when the 27-year-old plays well, so do Ulster.

There continues to be questions about the defensive side of his game, but his stats are strong as he has made 87% of his attempted tackles this season.

Calvin Nash

Like Stockdale, Calvin Nash is another player who has been in fine form this season and could have been in contention for selection regardless of who is fit.

Nash's sole cap to date came in the opening World Cup warm-up against Italy, where he was a late replacement in Dublin. He was released back to club duty after that game, but has kicked on with regular game time at Thomond Park.

He impressed last year as Munster won the United Rugby Championship final, starting in the final, and has carried that form into this season - scoring three tries so far.

Robert Baloucoune

One of the fastest players in the game, Robert Baloucoune has showcased his ability on the international scene, but injury after injury has held the 26-year-old back from earning more caps.

He has two tries in his four caps - including on his debut against the USA in 2021 - the 26-year-old will be eager to force his way back into Farrell's thinking.

Former Irish Sevens players Baloucoune is now getting a run of games with Ulster and although not as prolific in the current campaign as previously, he has improved the defensive side of his game with a 91% tackle success rate.

Jordan Larmour

There are similarities between Jordan Larmour and Stockdale, who both burst on to the scene but drifted out of the international picture in recent years.

The 26-year-old, who can operate on either wing and at full-back, has won 30 caps and was a 2018 Grand Slam winner but has not featured at international level since 2021.

He has been rediscovering his best form for Leinster this season, albeit in patches rather than being consistently at his best, but he is getting regular minutes and looks most comfortable in the 14 jersey that Hansen has been forced to vacate.

Best of the rest?

Farrell has plenty of options at his disposal if he wishes to look elsewhere for his Six Nations squad.

Ulster full-back Will Addison has spoken of his desire for an Ireland return after coming through a horrendous time with injuries, while the versatile Ulster back Michael Lowry has also impressed this season and is eager to add to his sole Ireland cap. In a wildcard shout, could Munster's Simon Zebo make a sensational comeback on the international stage, with his last cap coming in 2017 before he moved to France.

Shane Daly won two Ireland caps in 2020, so Farrell knows what he is all about, while Munster team-mate Mike Haley has a sole appearance in green to his name.

Or Farrell could opt for the inexperienced talent like Connacht's Diarmuid Kilgallen, who is his province's top scorer in the URC this season, would have been in contention if not for injury, but his Irish-qualified Springbok team-mate Shayne Bolton, returning Leinster wing Tommy O'Brien, or Ethan McIlroy, who has impressed for Ulster this season and is back in training after fracturing his cheekbone against Munster in November, could be in with an outside shot.

There has been a lot of talk about players making the switch to Sevens ahead of the Olympics, but what about the other way around? Andrew Smith was the Irish men's Sevens player of the year in 2023 and is getting more game time in 15s since joining Connacht from Munster in the last year.