London Irish hooker Agustin Creevy has been cited for allegedly pulling South African World Cup winner Eben Etzebeth's hair.
It follows Sunday's European Challenge Cup quarter-final between Irish and Toulon in France.
In a statement, tournament organisers European Professional Club Rugby said: "Creevy is alleged to have pulled the hair of the RC Toulon second-row, Eben Etzebeth, in the 35th minute of the match in contravention of Law 9.27 - a player must not do anything that is against the spirit of good sportsmanship."
Irish lost the game 19-18, with former Argentina captain Creevy now facing a hearing on Wednesday.
