A woman was sexually assaulted in woodlands near a housing estate in Northampton on Saturday night.
Police are now appealing for witnesses following the attack near Pine Close, Grange Park.
A spokesperson for Northamptonshire Police said: "The incident happened on Saturday, September 7, between 8pm and 8.15pm, when a man on a black bicycle approached a woman walking through thick woodland and grabbed her from behind.
"The man placed his arm across the woman’s shoulder and chest, pulling her towards him before grabbing her.
"The suspect is described as a white man, about 6ft, of chubby build and wearing a white hooded tracksuit top with a black zip and black goggles attached. He also wore a black balaclava covering his face and spoke with a local accent."
Anyone with information or anyone who witnessed what happened is asked to contact Northamptonshire Police on 101.