The London Legacy Development Corporation is considering its options after being ordered to reveal the full deal which will see West Ham occupy the Olympic Stadium from next season.
An information tribunal rejected the LLDC appeal against a London Assembly ruling that the contract between it and the Premier League club should be made public.
It means details of the funding for the Olympic Stadium, built for the London 2012 Olympic and Paralympic Games, must be published, amid suggestions of a lack of transparency over the use of public money in the project.
A spokesperson for LLDC, which is responsible for transforming venues used for the London 2012 Olympic and Paralympic Games, said: “We are disappointed by the tribunal’s decision.
“We have already published the vast majority of the contract and only undertook this appeal following very clear legal advice that to release the remaining details could significantly impact the stadium’s ability to act competitively.
“The ruling will result in significant challenges given the commercial realities of a highly competitive market, which could amount to many millions of pounds being lost over the term of a 99-year deal.
“We are considering the judgement very carefully before we decide on the next steps to take.”
LLDC could appeal against the decision.
West Ham were awarded tenancy of the 60,000-seat Olympic Stadium ahead of Tottenham and will leave their Upton Park home this summer.
The Hammers are due to move into the arena in time for the start of the 2016-17 Premier League season.
The venue is also to host the 2017 IAAF and IPC Athletics World Championships.
Olympic Stadium Coalition, a coalition of 14 supporters’ trusts and groups, has been campaigning for the contract to be published.
A spokesperson said on its website: “We’re naturally delighted with the outcome, as we see this as an issue of fairness to the taxpayer, to clubs near and far, and to football as a whole.
“We now respectfully request that the LLDC do what is right, waive the right to an appeal, and publish the deal in full so that it can be properly assessed and its implications understood.”