A disabled fan who booked an access ticket for R&B star Janelle Monae may not get a seat, she has been told.
Virginie Assal, who has a serious back condition, booked the ticket in 2018 so she could sit down, but the seats have now become "first come, first served".
She has to arrive early to get a seat at the 4 July concert at Manchester International Festival (MIF).
MIF said access was a "priority" and it had made adjustments to accommodate as many disabled people as possible.
However, it has emerged only provisions for wheelchair-users are guaranteed.
Ms Assal, who has a serious back condition and is the diversity and liberation co-ordinator at the University of Manchester, which focuses on inclusivity, says this is the first time a concert in the UK has not been accessible to her.
The 25-year-old said when she booked her ticket to see the popular US singer, who's just played Glastonbury, she was asked what she required - a seat away from the crowd - and was told "that was fine".
The situation changed last week when she looked at the festival's website and saw there were only provisions for wheelchair-users to reserve spaces and that seats for mobility impaired people could no longer be assured.
Ms Assal messaged MIF. In messages seen by the BBC, it replied: "We will have an accessible seating area available for the performance. As we have limited capacity, we'd advise turning up early as the seating area will be first come first served."
Ms Assal responded: "So booking an accessible ticket doesn't guarantee me to be in the accessible area? What time should I arrive?"
She was told the accessibility area has "unreserved seating" and is limited so she should arrive "as soon as doors open".
Ms Assal queried what happened if more people needed seats than were available.
"They won't get a seat," MIF responded.
"It made me upset," Ms Assal said. "How do I enjoy the concert now? I have scoliosis so my back isn't straight. It means I can't stand for a long time statically and I'm always worried in a crowd that I might get pushed and fall and really hurt myself.
"I really need a seat because it means I'm in pain if I don't have one and I don't really want to burst into tears because of the pain, or sit on the floor because of the pain, or put myself in a vulnerable position."
Ms Assal says she's now not sure whether to attend the concert at Castlefield Bowl, or not.
"I don't want to arrive early and get a seat and then find another disabled person has been turned away. I'd prefer them to have my seat."
Chris Fry, managing partner of Fry Law, which specialises in equality and human rights, says operating a "first come, first served" policy can be a breach of the Equality Act 2010.
Under the act, any organisation supplying a service to the public has a duty to make reasonable adjustments to ensure that a disabled person's experience is as close as possible to that of someone without a disability.
Mr Fry said it was the duty of the service provider, in this case MIF, to ensure the venue is accessible.
He said: "It's fairly well established that whilst 'first come first served policies' appear to offer a level playing field, if the outcome creates a systemic disadvantage to disabled people then they are a form of indirect discrimination and are unlawful.
"Whilst it's justifiable... for there to be a limit to the number of wheelchair spaces for evacuation and safety reasons, there's no reason why disabled people who do not use wheelchairs should be restricted to seating in those spaces."
In a statement to the BBC, MIF said: "MIF does not manage or run the venue. We have made reasonable adjustments within the constraints of an outdoor standing event, with limited capacity space, to accommodate as many disabled people as possible.
"We are not offering a 'first-come, first-served assistance policy' as suggested, we offer the same opportunity to book tickets and select access preferences to everyone."
MIF said it has 40 unreserved seats available for use in its access area at Castlefield Bowl.