A woman was left unconscious during an attack in Cambridgeshire which detectives said could have been an sexual assault.
The 27-year-old woman was walking in Peterborough on the cycle path running parallel to Gresley Way, Westwood at around 0320 BST on Tuesday.
A man grabbed her from behind and she hit the ground and fell unconscious.
A police spokeswoman said the victim had clothing removed but sexual assault tests have not been conclusive.
Officers said the woman was not seriously injured but extremely shaken.
The police spokeswoman added it was unclear whether the woman became unconscious when she hit her head on the ground or because the attacker had his hands around her neck.
The attacker is described as white, aged between 19 and 23-years-old, 5ft 7in (1.75 m) and of medium build.
He was dressed all in white including a white cap.
Det Insp Simon Harding said: "This attack left the victim very shaken and shocked.
"It is important anyone who was in the nearby area considers whether they saw the victim or her attacker, as that information could be crucial to this inquiry."