Greater Manchester Police (GMP) has joined the Football Association in investigating a smoke bomb that was thrown onto the pitch during Manchester City's Premier League win over Manchester United on Sunday.
The incident happened in the closing stages of the Manchester derby when a smoke bomb was thrown from the stands toward City's Bernardo Silva.
The object did not hit the City midfielder, landing a few feet away before being moved to the side of the pitch.
The FA has confirmed it is investigating the incident and has written to United to ask for their observations.
And GMP has now said it is looking to identify the perpetrator after the incident was reported to them.
A GMP spokesman said: "We can confirm that during the Manchester derby on Sunday police received a report that a smoke bomb had been thrown onto the pitch. An investigation has been launched and enquiries are ongoing."
The sides already have been given until 6 p.m. on Friday to seek their observations over the tunnel bust-up at the end of Sunday's clash.