Manchester United fans have been warned not to wear the club's colours when they are in Rostov, Russia, ahead of Thursday's Europa League tie.
United face FC Rostov in the first leg of their round-of-16 encounter this week, ahead of the second meeting back at Old Trafford on March 16, and the club are reportedly covering the cost of Russian visas for fans making the journey.
The Premier League club are concerned about the safety of their supporters, having issued a similar warning when they travelled to Ukrainian team Zorya Luhansk in December.
"For you safety and security you are advised not to wear Manchester United colours when in Rostov, or attract attention to you presence in the city," a letter sent by United's Head of Ticketing and Membership, Sam Kelleher, read.
"It is also advised you stay in groups where possible, and do not walk around the city alone.
"It is not just opposition football fans who may potentially pose a risk to your safety, and incidents of serious disorder during the European Championships in France last summer, involving violent individuals and groups emanating from Eastern Europe, should be remembered when considering your movements and actions, and any potential risk."
The Football Association (FA) will be sending an official observer with United to monitor supporter behaviour, match policing and the game itself. An FA observer was also present when United made a preparatory trip to Russia last week.
Russia fans clashed with England supporters at Euro 2016, while last week Russian politician Igor Lebedev proposed a radical idea of turning football hooliganism into a sport.