Manchester United have told supporters travelling to Tuesday night's Champions League clash against CSKA Moscow not to wear club colours for their own safety.
Around 2,000 United fans are anticipated in the Russian capital for the Group A showdown, with the club assisting by paying for their visas, reports the Manchester Evening News.
Liverpool are due in Moscow 24 hours later for their clash with Spartak.
United said in a statement: "All supporters must use the official bus service provided, and we ask that you ensure that your behaviour is impeccable at all times.
"The law enforcement authorities in Moscow are likely to be less tolerant than most other European police authorities, with a Police presence expected on-board each bus.
"There is no registration process for the bus transfers as all supporters have been catered for, therefore you will just need to show your match ticket in order to travel to and from the stadium.
"For your safety and security you are advised not to wear Manchester United colours when in Moscow, or attract attention to your presence in the city.
"It is also advised that you remain in groups where possible, and do not walk around the city alone, further highlighting the benefits of using the arranged bus transfers."
United's security warning comes as the head of Russian Football Union's security committee Vladimir Markin threatened to come down hard on troublemakers.
He said: "I don't want to scare anyone but I warn those who plan to come here not to support their side and see the country but to commit hooliganism: the law is the same for all, not just for Russians.
"Those who break it will face a suitable punishment, possibly in the form of a long stay in Russia, in conditions our guests won't like."