London - Manchester United warned supporters travelling to Rostov for Thursday's Europa League tie not to wear club colours or travel alone while in the Russian city, which will host World Cup matches.
The advice comes after England and Russia supporters were involved in violent clashes during last year's European Championships in France and Russian hooligans have said they will target English fans at the 2018 World Cup.
United's head of ticketing and membership, Sam Kelleher, sent a letter to supporters attending the last-16 tie, The Daily Telegraph reported.
"For your safety and security you are advised not to wear Manchester United colours when in Rostov or attract attention to your presence in the city," the letter said.
"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."