The Premier League have written to all 20 of their clubs advising them to be extra vigilant against the threat of a terrorist strike.
The letter was sent in the wake of last month's attack on a Berlin Christmas market that left 12 dead and 56 injured.
Manchester United, whose Old Trafford stadium is one of world football's iconic venues, have already stepped up their security measures. Following the twin attacks close to Besiktas's Vodafone Arena in Istanbul that killed 44 last month, United are checking vehicles that use club car parks for bombs.
One United fan, who was at the 2-1 win over Middlesbrough on New Year's Eve, said: 'My car was stopped and searched on the way in.