Leinster prop Jack McGrath has been handed a three-match ban for stamping on Ulster captain Rory Best.
The front row was ruled to have committed an act of foul play against his Ireland team-mate in last weekend's Pro12 game at the RDS.
McGrath will be eligible for the Six Nations opener in Rome on 7 February.
However, he will miss Leinster's Pro12 match against Cardiff on Saturday and the crucial European Champions Cup games against Castres and Wasps.
Leinster are expected to appeal against McGrath's suspension which will end on 25 January.
|Jack McGrath factfile|
|1989: Born, 11 October, Dublin|
|2009: Represents Ireland Under-20s|
|2010: Makes Leinster debut in Pro12|
|2012: Part of Leinster's Heineken Cup winning squad|
|2013: Makes Ireland debut against Samoa|
|2014: Helps Ireland beat South Africa and Australia in Autumn games|
McGrath was cited following last weekend's game and appeared before an independent disciplinary committee on Wednesday.
The committee ruled that McGrath's breach warranted a five-week suspension but reduced it to a three-game ban because of his previously unblemished record and conduct at the hearing.
Leinster are currently without their first-choice loose-head prop Cian Healy and McGrath's absence for the European games in particular will be a major blow to coach Matt O'Connor.
The incident occurred during the second half of Leinster's 24-11 victory over their provincial rivals.
McGrath, 25, made his first Leinster appearance five years ago against Glasgow Warriors.
His senior Ireland debut came against Samoa in 2013 and he has gone on to win 12 international caps.
In Healy's absence, McGrath started in both Ireland's wins over South Africa and Australia in November.