England skipper Owen Farrell could be ruled out of Saracens' European Champions Cup quarter-final against Leinster after he was sent off for a dangerous, head-high tackle in a Premiership match on Saturday.
The scores were level on the hour mark at Saracens' Allianz Park ground in north London when the fly-half was dismissed for a high hit on Wasps teenage back Charlie Atkinson.
The 18-year-old, making just his second start in the English top-flight, was left lying on the field for several minutes before being helped off the pitch.
Wasps went on to win the match 28-18 but reigning English and European champions Saracens' focus has long been on retaining the Champions Cup given they will be relegated at the end of the season for salary cap breaches.
Farrell, 28, expressed his remorse immediately but referee Christophe Ridley had little choice but to show the red card after the stand-off's arm connected with Atkinson's head.
While Saracens' salary cap offences are purely a Premiership matter, disciplinary punishments in one rugby union tournament traditionally apply across all competitions and Farrell could well now miss the last-eight clash against Irish province Leinster on September 19.
"I watched it live but have not watched it on the video," said Saracens director of rugby Mark McCall. "He was chasing his own kick and was desperate to make a tackle and clearly got it wrong and he got his red card."
The former Ireland international added: "It is what it is. He could easily have been out of the Leinster game for another reason -- injury or whatever.
"He missed the last quarter-final of the Champions Cup because his wife was having their first child. We have got plenty of good backs at the club so we will just rearrange our back line a little bit and get on with it.
"He works really hard on all parts of his game and he has improved in that area.
"Today's incident was a little bit different because he was chasing a kick and trying to make a difference to his team. We hope the player he hit is OK."
The tackling technique of Farrell, England's captain in last year's Rugby World Cup final defeat by South Africa in Japan, has long been a controversial topic.
In November 2018 Farrell, while playing for England, escaped any sanction for a shoulder charge on South Africa's Andre Esterhuizen when, with 80 minutes on the clock, a penalty would have given the Springboks a chance to kick for goal in a match they lost 12-11.
Three weeks later, Farrell's no‑arms tackle on Izack Rodda also went unpunished in the victory over Australia, with the Wallabies furious at not being awarded a penalty try.