England captain Farrell risks being banned for Six Nations opener
The Saracens fly-half, 31, is in line to start for England in what will be new head coach Steve Borthwick's first game in charge, against Scotland at Twickenham on February 4th.
But he could be sidelined match following what appeared to be a high, shoulder-led charge on Gloucester replacement Jack Clement near the end of a tense encounter at Kingsholm, where Farrell landed a winning drop-goal with the last kick of the game.
Match referee Karl Dickson took no on-field action against Farrell, after what appeared to be a miscommunication with the television match official. Citing commissioner James Hall could decide Farrell, the last England captain appointed by former coach Eddie Jones, has a case to answer after the stand-off's shoulder made contact with Clement's chin.
Mid-range dangerous tackles, including contact to the head, come with a six-week ban, which can be halved with a good disciplinary record. Suspensions can also be reduced if offenders agree to undergo a course in improving their tackling technique.
Farrell was banned for five games in 2020 following a high tackle on Wasps player Charlie Atkinson, and questions about his technique have been raised before, notably when he escaped sanction for a shoulder charge on South Africa's Andre Esterhuizen at Twickenham in 2018.
Punishments for suspensions incurred at domestic level in rugby union can also be applied to international matches.
Borthwick, among the crowd at Kingsholm, will now be awaiting developments, with an announcement about whether Farrell will be cited expected Monday.
Asked about the Clement incident, Saracens rugby director Mark McCall said: "I was pitch-side for the last three or four minutes, so I haven't seen it yet.
"I have heard there is a potential high tackle that I will have to look at."
Gloucester coach George Skivington added: "It is really tricky to comment on it. I don't want to end up in a judiciary myself, so I have to keep shtum.
"I will just say that consistency across games will be good."