Arsenal are launching an investigation over a row between the Manchester United bench and fans during Saturday's defeat. The Daily Star says United substitute Darren Fletcher and others on the visitors' bench were furious after red wine was allegedly thrown.
Fletcher exchanged words with Arsenal supporters a few rows behind the dug-out at the Emirates.
The incident came after Kieran Gibbs scored an own goal to put United 1-0 up in the 56th minute.
Former United boss Sir Alex Ferguson previously complained about the lack of protection for away teams on the bench at the Emirates.
United are understood to be happy with the way their rivals are handling the flashpoint but have not ruled out making an official complaint.
Arsenal have confirmed a man was arrested following the incident and that they were fully co-operating with the Metropolitan Police.
"We do not tolerate anti-social behaviour. If found guilty, the individual will also be banned by the club," said a spokesman.
