Police are working with Arsenal to identify the fan who threw a plastic bottle at Tottenham's Dele Alli during the Carabao Cup tie between the north London rivals at the Emirates.
The incident occurred in the 73rd minute of Wednesday night's clash while England midfielder Alli, who had just scored Spurs' second goal, was taking a throw-in.
In a statement, a Metropolitan Police spokesperson said: "The Met is working with Arsenal Football Club to identify the person responsible for an incident where a bottle was thrown onto the pitch during the Arsenal vs Tottenham match on Wednesday, 19 December.
"There has been no arrest in relation to this specific incident.
"Seven people were arrested as part of the policing operation for this match for a variety of offences including possession of drugs, public order and assault on police."
The bottle struck Alli on the head, but the 22-year-old was not hurt and reacted by making a 2-0 gesture to the home fans, which was how the game ended, sending Spurs through to a semi-final against Chelsea.
After the game, Alli told Sky Sports: "It is what it is – it made the goal a bit sweeter and the win."
The Football Association has confirmed to Press Association Sport that it is also investigating the matter but it is up to the police and club to try to identify the culprit and make sure they face the appropriate sanction, which will almost certainly be a ban.
Arsenal have not yet responded to a request for comment but it is understood they are reviewing CCTV footage to find the person responsible.
Former Gunners striker Ian Wright believes the fan should face a strong punishment.
He told his YouTube channel: "I've got to roundly condemn the person who chose to throw something at Dele Alli.
"I know Dele can be a bit of a pantomime villain but it's no excuse. I did exactly the same to the Spurs fans and I don't ever remember having anything thrown at me.
"Whatever the club is doing they should fine that person, ban them, ban them for life. We don't want that attached to our club."
A Spurs fan was arrested for throwing a banana skin at Pierre Emerick-Aubameyang when the two teams met in the Premier League at the start of the month.
He was handed a four-year football banning order on Wednesday after pleading guilty to throwing a missile.