FIFA has confirmed to Sky Sports it is investigating whether Robbie Brady threw a headbutt at Wales defender Ashley Williams.
The incident took place in the 61st minute of the Republic of Ireland’s 1-0 win in Cardiff and was missed by referee Damir Skomina.
A FIFA spokesperson said they are in the process of collating evidence to see whether Brady should be charged.
If he is, Brady could miss at least the first leg of their World Cup play-off next month.
The Burnley midfielder only returned from a one-match suspension for their must-win match in Cardiff, where James McClean’s 57th-minute strike secured second place in Pool D.
Ireland will definitely be without stand-in skipper David Meyler for the first leg of their play-off, which is due to take place between November 9 and 11.
Hull City midfielder Meyler was booked in injury-time for a challenge on Wales goalkeeper Wayne Hennessey. It was his second yellow card of the World Cup qualifiers which earns him an automatic one-match suspension.
The draw for the World Cup play-offs takes place on October 17.