Concerns have been raised that the decision to cut the away allocation at Tuesday night's Manchester derby on safety grounds may actually end up triggering trouble.
Last month, in a controversial move, United and City decided to slash the number of tickets available for away fans for each leg of their Carabao Cup semi-final.
Each club has been given a visiting allocation of around 3,000 – far less than what they were entitled to under competition rules.
The first leg takes place at Old Trafford on Tuesday night, but United have struggled to sell out.
Tickets are now effectively on open sale – prompting fears that City fans will take the opportunity to buy seats in home sections of the stadium, with the potential for a similar scenario unfolding at the second leg.
The situation has led the Manchester United Supporters Trust (MUST) to hit out at what they say was a lack of consultation over the original decision.
'A key risk that we identified was the likelihood of away supporters, denied seats in the reduced away sections, seeking tickets among home supporters,' a spokesperson said. 'We would of course have raised that major risk proactively had we been consulted.'
Under normal rules, City would have been entitled to around 7,000 tickets at Old Trafford and United 5,500 at the Etihad.
MUST have also pointed out that substantial visiting allocations (15 per cent of stadium capacity) were handed out at both the recent Liverpool v Everton and Arsenal v Leeds FA Cup matches.
'It is legitimate to ask why Liverpool and Arsenal are confident in their ability to manage these larger allocations safely but United and City are not,' the MUST spokesperson added.
The reduction is understood to have been agreed on the back of a number of incidents in recent derbies. Both clubs felt that significant increases in allocations could 'potentially increase the risk of disorder'.
There will be an increased police presence at Old Trafford and United say any away fans spotted in – or trying to gain entry to – home areas will be dealt with.
'We have a series of measures in place to minimise security risks,' a United spokesman said. 'Anyone visibly or audibly supporting the away team in home areas will be denied entry or ejected.'