Joey Carbery is almost certainly out of Leinster's return fixture against Northampton Saints and could miss the Christmas interprovincials as a result of the ankle injury he suffered on Friday night.
Leinster are awaiting confirmation of the damage and will issue a bulletin on the young Ireland international's prognosis today, but it looks likely that Ross Byrne will lead their backline for the rest of December.
The 21-year-old is the only fit No 10 in Leo Cullen's European squad as Johnny Sexton is going through an extended rehabilitation in Santry in an effort to correct his hamstring problems and Cathal Marsh is out until the new year as he recovers from hand surgery. Isa Nacewa and Noel Reid could deputise.
Byrne replaced Carbery after 12 minutes at Franklin's Gardens and guided his side to a 37-10 win on his first European appearance, overcoming a nervy start to nail a confidence-building cross-kick for Rory O'Loughlin's try.
He finished the game needing stitches, but did not incur any further damage.
A star of the 2015 Ireland U-20s side, his progress has stalled due to a succession of injuries but he has always been rated highly within Leinster and now has his chance to stake his claim.
Saturday's Aviva Stadium return clash with Northampton will be his fourth senior start.
Leinster have also confirmed that Seán O'Brien passed a head injury assessment (HIA) after he was on the end of Dylan Hartley's swinging arm on Saturday night, but the flanker will continue to be monitored as a precaution. Rob Kearney is expected to be fit.
Hartley will almost certainly be banned for the return, while JJ Hanrahan and Jamie Elliott are major doubts for Northampton who will welcome back suspended pair Kieran Brookes and Calum Clark for the Aviva Stadium clash.
'Remember 2013' will be the message coming out of Leinster this week as they attempt to ward off complacency ahead of Saturday's re-match.
Many of the current squad weren't involved when Jim Mallinder's Saints dusted themselves off after a 40-7 hammering at Franklin's Gardens and ended the three-time European champions lengthy winning run at the Aviva Stadium, but they will know all about it by the time Saturday rolls around.
"It's something we're very conscious of. Northampton are a proud club so they will come back strong," Cullen said. "We expect a physical challenge next week so we need to have our heads on."
Sometime last season, after writing a piece on Dylan Hartley's unending thuggery on the rugby field, the player responded by calling me a snake. My psychiatrist tells me I may recover from this in a few years - I'm not so sure though. The sleepless nights, the panic attacks, the sense of emptiness. I'm not sure whether I will ever recover.
England face an anxious wait to discover captain Dylan Hartley will miss the start of the Six Nations Championship after he was sent off just six minutes after he returned to club duty.
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