Owen Farrell's dangerous challenge on Charlie Atkinson was "an accident waiting to happen", according to former Ireland and Lions manager Donal Lenihan.
The England captain was sent off for the first time in his career while playing for Saracens against Wasps in the Premiership on Saturday, with the subsequent five-game suspension ruling him out of the Heineken Champions Cup holders' meeting with Leinster on 19 October in Dublin.
Out-half Atkinson, 18, was knocked out and has been stood down for "a couple of weeks" said his club.
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"Saracens have been focused on this quarter-final for the last five or six months," Lenihan, speaking on the RTÉ Rugby podcast, said.
"They have been chopping and changing their team in the Gallagher Premiership, which, of course, is meaningless for them for them as they've already been relegated.
"All roads were leading to Dublin.
"Owen Farrell, it was only a matter of time before he was going to get in serious trouble over a high tackle.
"Apparently, he’s had eight yellow cards in his career, seven of them have been for high tackles so this was an accident waiting to happen. It looked a dreadful tackle.
"He does get a bit of red mist if things don’t go his way, we have seen that before. I don’t think there’s any badness or malice in him, he’s the ultimate competitor.
"The recipient was an 18-year-old just out of school so it wasn’t a great ad for the game.
"It's a really bad one... I can't defend that."— Rugby on BT Sport (@btsportrugby) September 5, 2020
Owen Farrell was shown a red card against Wasps for this tackle on Charlie Atkinson...
Lawrence Dallaglio considers the implications for Saracens AND England. pic.twitter.com/xZuOfEZK9E
Leinster have to negotiate a Guinness Pro14 final against Ulster on Saturday before focus will turn to regaining the title they last won in 2018.
The absence of 28-year-old Farrell, who has 83 England caps, has to come as a boost for Leo Cullen’s side, notwithstanding the strength in depth of the Saracens squad. Alex Goode or Manu Vunipola will come in for Farrell.
"For a player of his experience, quality, given his role as captain he just needs to exert some more self-control and it’s cost the club very dearly now," added Lenihan.
"It’s not going to be a straightforward game for Leinster but for Saracens to be without their key man at number 10 is huge."
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Follow the Pro14 final between Leinster and Ulster Munster (7.35pm Saturday) with our live blog on RTÉ Sport Online and the RTÉ News app or listen to live commentary on RTÉ Radio 1.