Dele Alli could face a ban after showing his middle finger during England's win over Slovakia.
The Tottenham midfielder appeared to react to a challenge from Martin Skrtel by "flipping the bird" in the direction of the former Liverpool defender.
Alli - who toiled hard over the 90 minutes of England's 2-1 win before being replaced by Jake Livermore in stoppage time - appeared to be angered by a challenge in the 76th minute at Wembley.
There are also suggestions it was actually aimed at the referee.
And England manager Gareth Southgate claimed he was showing it jokingly to team-mate Kyle Walker, something that was backed up by the player himself.
Alli and Walker were also teammates at Tottenham until the latter joined Manchester City for £52million this summer.
Whoever the target, Alli could face a ban if the incident is reviewed by UEFA.
When Southgate was asked about immediately after the game, he said: "I didn't know about it it until you told me just now.
"We will have a look at it in the next couple of days."
But he later added: "Dele and Kyle were mucking about and maybe Dele has gestured towards Kyle.... they have a strange way of communicating."
And Alli tweeted: "Just to clarify, the gesture tonight was a joke between me and my good friend Kyle Walker! Apologies for any offence caused! Great win 2nite."
ITV pundit Lee Dixon added: "If the ref has seen it and it is in his report then he's in trouble."