Learning Through Landscapes stands to lose £500,000 after three of its funders reviewed their grant priorities in light of the Government's Building Schools for the Future scheme.
Three charitable trusts have written to the school playgrounds charity, saying they understand that large amounts of money are now available for schools as part of the Department for Education and Skills' programme to modernise the infrastructure of English schools.
However, Learning Through Landscapes chief executive Ken Davies insisted that this money is for buildings only, not for school grounds.
Davies said the Government's well-publicised programme had created the false impression that playgrounds do not need funding any more. He said that losing support from the trusts would not be a major blow for the charity because it receives significant funds from the private sector.
But he said he feared this misconception might spread among charitable trusts, which would hit schools hard. "We are talking about hundreds of organisations, and if this becomes a general perception it will have a big impact on outdoor spaces," he said.
Funding for playground improvements was previously available through the New Opportunities Fund's PE and Sport scheme, but this initiative is closing following the creation of the Big Lottery Fund. It will be replaced later this year by a £155m programme for playgrounds.