An investigation has been launched after a 26-year-old man suffered burns to face and may lose sight in one of his eyes after being sprayed in the face by substance outside Bounce Bar on Old Street in the early hours of 17 September.
The suspect had earlier attempted to sell nitrous oxide to the victim and his friend earlier in the night. The pair declined and all three then got into an argument.
At around 5:25am, the two men came across the suspect again. As they walked past him, the suspect sprayed a substance at the victim, with a small amount of liquid hitting his friend.
The 26-year-old went to a nearby shop to douse his face with water before being taken to an east London hospital suffering burns to his face. Tests are being carried out to determine what the liquid used in the attack was.
Police have now released CCTV footage of a man they want to speak to in connection with the attack.
The suspect is described as being of middle-eastern or a light-skinned black male in his mid to late 20s, around 6ft tall and of normal build. He was wearing dark clothing and a Gucci belt with a gold buckle.
DC Dave Barrett of Hackney Police, said: "This was a violent, unprovoked and cowardly attack by a troublemaker who has left his victim with life-changing injuries.
"We would urge anybody who recognises the man in the picture, or who was in the area at the time and may have information that could assist our investigation to get in touch."
Any witnesses or anyone with any information is asked to call Hackney police on 101 or contact via Twitter @MetCC.
To give information anonymously contact Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org