A 60-year-old tourist was left needing surgery after she was attacked by a man in his 20s - who failed to chat her up.
The Austrian woman, who does not want to be named, was approached by the much younger man who struck up a conversation.
He unsuccessfully tried chatting her up, according to Met Police, before launching a brutal assault.
The incident happened at around 8pm on March 10 near Warwick Avenue tube station in west London.
The suspect followed the victim, grabbed her from behind and seriously assaulted her by repeatedly punching her in the face, leaving her with shocking facial injuries.
A passer-by found the victim a short time later and called the emergency services, who took her to hospital for treatment.
She has since been discharged but will require further surgery.
The suspect is described as a white man, aged around 25 to 27 years, about 5ft 8ins tall with short brown hair and brown eyes.
He was wearing light coloured trousers, a brown jacket and a black baseball cap.
Detective Constable Mike Reilly, the investigating officer from Westminster CID, said: "This was a vicious unprovoked attack that has left the victim very shaken. Her injuries are so severe that she requires surgery.
"Warwick Avenue is a busy area, especially at 8pm on a Friday evening.
"Someone must have seen something and I'd appeal for anyone with information to come forward as soon as possible so we can bring the perpetrator to justice."