The Swiss was given a booking by referee Andre Marriner for time wasting in the 86th minute of the December game.
The FA initially opened an investigation into the incident in January and they have now referred it to the National Crime Agency, reports the Daily Mail.
The report claims the escalation comes as a result of a development which indicates serious concerns over corruption and possible criminality.
The report states that an unusually large bet of £52,000 was placed during the match that required Xhaka to be booked in the final 10 minutes. At that stage, Leeds were already losing 4-1.
The Mail say there has never been any suggestion of any wrongdoing by Xhaka or any other Arsenal player.