Arsenal goalkeeper Jens Lehmann faces a police probe after he was accused of kicking a water bottle at Manchester United fans.
The German international was accused of booting the bottle into the East Stand during Sunday's Premiership match at Old Trafford.
A police spokesman said: 'Greater Manchester Police have received one complaint in relation to an allegation that a water bottle was kicked into the crowd during the Manchester United v Arsenal match on Sunday 17 September.
'It is alleged the bottle was kicked from the pitch into the East Stand.
'Officers are investigating the allegation and inquiries are ongoing.'
The high-tension match finished 1-0 to Arsenal after a late goal from striker Emmanuel Adebayor.
Earlier, Lehmann was hit in the face from close range by a shot from United winger Cristiano Ronaldo.
He was knocked down and took several minutes to recover, before making an impressive save at the end to retain Arsenal's lead.
The rivalry between the clubs has led to aggression both on and off the pitch in recent years.
In 2004 slices of pizza were thrown in the players' tunnel after Arsenal lost 2-0 at Old Trafford. The incident became known as the 'Battle of the Buffet'.
Arsenal defender Martin Keown was fined £5,000 after his spat with United striker Ruud van Nistelrooy during Arsenal's 2-0 defeat in December 2002.