United boss Sir Alex Ferguson has previously admitted he cannot tell the difference between the Brazilian twins Fabio and Rafael, but he is not the only one.
Foy booked Fabio for a foul on Barnsley sub Jamal Campbell-Ryce in the second-half of United’s 2-0 win.
But it was actually Rafael who has committed the offence.
A United spokesman said: “We are in discussions with the FA over this matter.
“We have pointed out that the referee made a mistake on the night and we obviously want it to be corrected.
“We will be asking for further advice on how best to rectify the situation.”
