On Saturday Millwall head across London to Queen's Park Rangers, with dark threats having already been made by Chelsea followers in the wake of the pitch invasion which followed Millwall's fourth-round penalty shoot- out victory at Stamford Bridge.
And 24 hours later police will be on full alert as Leeds make the short trip across the Pennines to Manchester United to renew one of the fiercest supporters' rivalries in the country.
While all four clubs and the police are hoping for incident-free afternoons, there is little attempt to downplay the possibility of more trouble.
Millwall, with only 3,000 tickets for the game at QPR, will be screening the match live to fans at The New Den, while Leeds' allocation of 6,500 seats at Old Trafford has been sold strictly to Elland Road members.
But as Superintendent Paul Lally, the man in charge of policing at Loftus Road, conceded, the efforts of the clubs could be undermined by thugs bent on violent confrontation.
"I gather Millwall have already sold 5,000 tickets for the screening at The Den but I fear they will be the genuine football supporters and not the people out to cause trouble," he said.
"If anything, it might keep some of the troublemakers away," he said. "If football violence has a high profile it means the courts are inclined to take a more serious view."
The Leeds secretary, Nigel Pleasants, said every step had been taken by both clubs and police to ensure a trouble-free afternoon.
"We could have sold our tickets many times over but they were restricted to members who know that if they misbehave they will have their membership taken away," he said.Reuse content