Greater Manchester Police are investigating an allegation of common assault against Jose Mourinho following last night's Champions League tie between Manchester United and Inter Milan at Old Trafford.
It has been alleged Mourinho punched a supporter close to the Inter team bus as he left the stadium following his side's 2-0 defeat.
GMP have contacted United to request CCTV footage of the area and have confirmed a complaint has been made.
"Shortly before midnight last night a man reported that he had been punched in the face outside Old Trafford," a police statement read.
"We are investigating an allegation of common assault."
United would only confirm they are aware of the allegation and are making no further comment.
The allegation came at the end of a bad night for Mourinho, who watched his team crash out of the Champions League following their defeat, with Nemanja Vidic and Cristiano Ronaldo grabbing United's goals at the start of each half.
Although the former Chelsea manager was in jovial mood, shaking hands with Red Devils supporters as he made his way to the visitors' dug-out before kick-off and after half-time and enjoyed a friendly post-match chat with Sir Alex Ferguson, he came under sustained attack from the Italian media for his failure to get Inter through.
"If anyone wishes to criticise my team, they will have to fight me," he said at one point, those comments coming via an official interpreter from Italian.
Although he has taken Inter to the top of Serie A, his relationship with the local press is far from smooth, a fact that has only fuelled a belief that he could one day replace Ferguson at Old Trafford.
The plane taking the Inter party back to Milan left Manchester at 12.25am last night, once Mourinho had concluded his post-match obligations and enjoyed his ritual of a meeting with Ferguson.