Manchester United have threatened to ban fans if tickets are passed onto rival City supporters for Tuesday's Carabao Cup semi-final.
The away allocation for both Manchester derby ties have been cut from 6,000 to half that number following police advice.
But tickets for the first leg at Old Trafford went on general sale which raised fears away fans would buy seats in home sections.
United are confident of avoiding a repeat of fan violence which marred the last League Cup semi clash in 2010 as well as December’s derby when missiles were thrown from the stands at the Etihad and United players were subjected to racist abuse.
But the Red Devils sent an email to their supporters which read: “It is important to note that:
All tickets must be used by Manchester United supporters.
Any tickets found in the possession of away fans will be cancelled without refund and the ticket holders will be ejected.
Any instances of tickets being passed to away supporters will be handled in accordance with our Official Club Sanctions policy, and the registered ticket holder will be suspended from purchasing or attending home and away matches.”
Some critics have expressed surprise that United have put tickets on general sale for Tuesday’s first leg at Old Trafford.
But United believe they have measures in place to minimise the risk of a repeat of the trouble that marred the Premier League game at the Etihad last month - and the larger-scale issues of 10 years ago.
Back in January 2010, police made a number of arrests for violent disorder and other offences following clashes between rival supporters at the first leg at the Etihad.
Despite calls for calm, in the return game at Old Trafford, City striker Craig Bellamy was struck by a coin and a bottle was also thrown.
A decade later, the two clubs have consulted with police and agreed to reduce the number of tickets available to away supporters from the normal level of 6,000 to 7,000 to just 3,000.
United believe extra police and stewards on Tuesday night, in conjunction with hi-tech surveillance via CCTV, will deter potential troublemakers and easily identify those who misbehave.
Sales of tickets to non-members have been restricted to two per person and putting them on general sale is standard policy at Old Trafford for Carabao Cup matches.
United felt it was a greater risk to allow thousands more away fans into the match than to leave open the possibility that rogue visiting supporters would buy tickets in home sections.