The man approached the 35-year-old woman from behind and touched her indecently.
The incident happened at 6.30pm on Monday, March outside the Sacred Heart church in Mere Road, Highfields.
The victim has worked with police to create the image, known as an e-fit, of her attacker.
Detective Constable Stu Palmer said today: “If you witnessed the incident or you recognise the image then we need to speak to you.
“This was an extremely distressing incident for the victim and we need to catch the person responsible.
“If you have been approached in similar circumstances or you know anything about the incident then please get in touch.”
The suspect is a fair skinned Asian man, approximately 20, of medium build and 5ft 5ins to 5ft 7ins.
He was wearing clear slim-rimmed glasses and a white shin-length Islamic robe.
Contact Det Con Palmer on 101 or Crimestoppers, which is anonymous, on 0800 555 111.