The Daily Post has learned that Liverpool Council was awarded the first £1m of a £4.8m Heritage Lottery Fund (HLF) grant for the park - but withdrew its bid in June, 2001, when Liverpool FC came forward with its £80m stadium proposal.
Campaigners fighting the stadium plan branded the rejection of the grant "a disgrace" last night, and said they had asked the district auditor to investigate.
The council is planning to put in a new £5m grant application to the HLF later this year, but there were indications last night that the football stadium proposal could jeopardise the bid.
Tony Jones, HLF's regional manager in the North West, has told the Daily Post that a proposed funding application could be turned down if the new stadium was built there. The warning comes with less than a month to go to the deadline for objections to the stadium plan. In January, 1999, before the stadium proposal came up, the council made a bid for £4.8m for the park to the HLF, and around £1m was given "in principle" for a first phase of work.
Mr Jones said: "Liverpool City Council had ambitions for major bids in three parks, Sefton, Stanley and Newsham.
"Around £1m was awarded in principle to Stanley Park. What then arose was the football club possibly moving into the park.
"At that stage, Liverpool city council and HLF both thought that could have major implications for the park.
"After discussions, it was agreed in June, 2001, that the council should with-draw the bid."
Chairman of the Friends of Stanley Park George McLennan said: "I was part of the original project team which secured the £1m grant.
"Then the football club idea came about and HLF kept asking the council where it was up to, but they just couldn't give them any answers so we lost it."
The chairman of the Anfield Regeneration Action Committee, Joe Kenny, said: "An area like Anfield can ill afford to be turning away £1m of vital funding.
"It is an absolute outrage and it will be an even bigger disaster if a further grant is jeopardised. This is not just about our heritage but about saving the park for future generations."
It is expected that a renewed bid for a £4m-£5m grant for Stanley Park will be made later this year, but the football club could still prove to be a major stumbling block.
Liverpool Council leader Mike Storey said he remained confident that the new bid would succeed.
A city council spokesman said: "There was an 'in principle' agreement back in 1999 for a £1m grant but our understanding was that the HLF withdrew that when the situation surrounding the stadium arose."