Windsor Girls' School had their £1.3m plans to build new facilities, including four badminton courts, changing rooms and storage areas, approved in March and hoped to open the 612sq m sports hall next year.
The improvements will be part funded by the sale of a 'small corner' of land owned by the Imperial Road school, but changes by the Department of Education to its Outdoor Space policy mean the sale will have to be deemed 'suitable' by the Secretary of State.
Speaking at a Children's Services Overview and Scrutiny Panel meeting on Monday night, councillor Lynne Jones said: "The problem that is going to cause a difference of opinion is the word 'suitable'. To what standard is that? Until the Government defines that then I am sure there will be lots of chatter about this."
In theory the Government changes, which come into effect at the end of October, should give schools and authorities more flexibility with their land.
Secondary schools previously had to provide pitches ranging from 5,000sq m to 54,000sq m, but that requirement has been replaced with 'suitable outdoor space'.
Councillor Eileen Quick, cabinet member for education, said: "I hope it is not going to have an effect on the sale of a very small amount of land at Windsor Girls' because it is going to fund a sports hall."
Cllr Quick said should the worse case scenario emerge and the Government reject their proposals, the council has drawn up a contingency plan.
It is proposed the Royal Borough gift the school a piece of neighbouring council-owned land to appease any Government concerns.
Cllr Quick added: "We have got a way of overcoming it in this case, but whether we will do in the future I do not know. My inclination is it will actually make it easier for schools and authorities to move land, but until there is more detail we do not know."