The game clashes with a general strike that has been called in Spain for that day that threatens to cause travel chaos around the country.
UEFA were aware of the situation at an early stage but having given indications they would turn down any request to move the fixture, United have been left with little alternative other than to hope a resolution can be found.
Although any disruption should not affect Sir Alex Ferguson's travel plans, supporters are likely to experience major problems, especially those intending to travel out on the day.
United have posted warnings on their official website but up to this afternoon there had been none on the site of Thomas Cook Sport, the club's new travel partner, who are responsible for the official trips many fans choose to go on.
This has led to criticism from the Manchester United Supporters' Trust, who have accused Thomas Cook Sport of being "reluctant to lose lucrative bookings" rather than pay out refunds to supporters wishing to make other plans themselves.
MUST claim that Thomas Cook Sport receive huge numbers of tickets in return for their sponsorship payment, which makes it less likely those who wish to travel independently will get into the game.
This, MUST argue, is the fault of the Glazer family, who they state are more interested in "getting their sponsorship money from Thomas Cook than looking after their most loyal fans".
However, Thomas Cook Sport have denied the allegations, and in a statement released on Friday and posted on the organisation's website this afternoon, insist they are monitoring events closely.
"We take any threat of action that may impact on travel plans extremely seriously and we are monitoring the situation closely," said a spokesman for Thomas Cook UK and Ireland.
"Should any strikes be confirmed, fans will be able to get all their money back or take advantage of alternative travel arrangements which we're already considering."
A spokesperson for Manchester United added: "We are constantly in touch with UEFA on the possibility of a general strike in Valencia on September 29 and we will keep fans up to date through our website and work with Thomas Cook on travel plans."