Manchester United has condemned an "unwarranted attack" on the home of one of their employees, amid reports flares were thrown at the residence of executive vice-chairman Ed Woodward.
Social media videos appear to show hooded attackers outside a property, throwing flares over the gate.
In a statement, United said anyone found trespassing on the property faced a life ban from the club and may be prosecuted.
"Manchester United Football Club has tonight been made aware of the incident outside the home of one of our employees," a spokesman said.
"We know that the football world will unite behind us, as we work with Greater Manchester Police to identify the perpetrators of this unwarranted attack.
"Anybody found guilty of a criminal offence or found to be trespassing on this property will be banned for life by the club, and may face prosecution.
"Fans expressing opinion is one thing, criminal damage and intent to endanger life is another. There is simply no excuse for this."
It is unclear whether Woodward was inside the property during the attack.
Woodward and club owners - the US-based Glazer family - have been the targets of verbal abuse from fans at the last two United matches.
United are the record 20-time England champions, but haven't won the Premier League since 2013 and are struggling to seriously challenge for big trophies.
Woodward, who is married with two young children, has been blamed for United's recent troubles, because he effectively runs the club's day-to-day operation and oversees recruitment.