Glasgow's Ryan Wilson has been cited after being "alleged to have grabbed the testicles" of Northampton scrum-half Lee Dickson.
Under World Rugby's laws, which cover "testicle grabbing or twisting or squeezing", Wilson could also face a lengthy ban at a hearing on January 20.
Wilson's Glasgow team-mate Tim Swinson will have a hearing on the same day after he allegedly punched Northampton hooker Mikey Haywood in the 74th minute of their 19-15 defeat at Franklin's Gardens in the European Champions Cup on Sunday.
Newport replacement hooker Rhys Thomas has also been cited after he was alleged to have bitten Castres back row Thomas Caballero in their European Challenge Cup clash.
The 33-year-old allegedly bit Caballero in the 67th minute of Newport's 31-18 win over the Top 14 side on Friday.