Alan Quinlan has been handed a 12-week suspension by an independent ERC disciplinary committee after he was found guilty of making contact with the eye area of Leo Cullen during Munster's Heineken Cup semi-final meeting with Leinster.
The ban threatens his place on the Lions tour to South Africa and the Munster forward now has 72 hours in which to lodge an appeal following written confirmation of the suspension by the disciplinary committee.
Lions head coach Ian McGeechan must now consider a replacement, with Leicester and England flanker Tom Croft favourite to come in should Quinlan be ruled out.
Quinlan, 34, becomes the third player selected in a 37-man Lions squad last month to be ruled out.
Quinlan's Munster colleague, scrum-half Tomás O'Leary, broke his ankle three days after the party was announced and has subsequently been replaced by Scotland skipper Mike Blair.
Wales centre Tom Shanklin then suffered a serious shoulder injury - like O'Leary, he was also on Magners League duty - and faces four months out. Shanklin's replacement has not yet been announced.
Quinlan, capped 27 times by Ireland and man of the match when Munster beat Toulouse in last season's Heineken Cup final, had won a Lions call-up partly due to his abrasive, no-nonsense playing style.
But his tour hopes ended following an appearance before a three-man independent disciplinary panel, chaired by Welshman Roger Morris, in Dublin today.
Quinlan was reported by match citing commissioner John Byett following the Cullen incident, which had been graphically captured on television slow motion replays.
The panel, which also comprised Morris' fellow Welshman Simon Morris and England's Mike Hamlin, decided Quinlan was guilty of Law 10.4 (an act contrary to good sportsmanship) in that he made contact with Cullen's eye area.
At the end of a lengthy hearing, the panel decided Quinlan's offence was at the low-range of the level of seriousness for such an offence, and banned him from today until 10 September.
McGeechan's Lions squad assemble in Surrey next Monday. They fly to Johannesburg six days later, and play their opening game against a Royal XV in Rustenburg on 30 May.
The 10-match trip culminates with three Tests against world champions South Africa in Durban (20 June), Pretoria (27 June) and Johannesburg (4 July).
If Quinlan decides to appeal, it is likely any hearing would take place within the next week.