UEFA are reportedly investigating a Twitter account suggesting that referee Cuneyt Cakir, who officiated Manchester United's defeat to Real Madrid in the Champions League, is a fan of the Spanish giants.
The Turkish match official has come under scrutiny for controversially sending off United winger Nani for a high challenge on Alvaro Arbeloa, which led to a 2-1 victory for Madrid at Old Trafford on Tuesday night.
The Twitter account in Cakir's name is thought to be following 38 people, including Madrid star Cristiano Ronaldo and the club's official page.
"We are aware of it and are looking into it," a spokesman told the Daily Star. "First we need to establish if it is genuine and has not been interfered with. Then we will consult with our referees' unit to see if any rules have been breached."
If true, the referee could be in breach of the European governing body's guidelines on impartiality.