Clair Park in Haywards Heath was closed off by police for several hours yesterday due to a suspected assault.
Police tape was seen around the trees at the top end, above the play area – and all entrances were shut off by officers.
A police helicopter was also spotted nearby.
A spokesman for Sussex Police said: “Police are currently investigating a third party allegation of an assault in Haywards Heath.
“Officers attended Clair Park on Monday afternoon (July 1), after a member of the public was approached by a woman, disclosing she had been assaulted.”
Detective Inspector Sally Arbuckle said: “This is a third party report where the woman left before disclosing any personal details or where or when the assault took place.
“An area search was conducted by officers but the woman was not found. If you are this woman we are urging you to come forward to us to ensure the relevant support can be provided.”
Anyone with information is asked to report online or call 101 quoting 977 of 01/07.