The incident happened at about 7am on Friday, August 7, in the woods on Granville Road in Donnington Wood.
The suspect is described as in his 30s, of a stocky build and wearing a light blue or grey T-shirt and light blue or grey jogging bottoms or shorts.
Police are carrying out enquiries and appealing for witnesses.
Anyone with information should contact West Mercia Police on 101 or under the Tell Us About section at westmercia.pnn.police.uk
Alternatively contact Crimestoppers anonymously on 0800555111 or crimestoppers-uk.org