Detectives say a man in his 40s was walking home at around 12.45am on Monday when he was assaulted by a group of four males near Bryn railway railway, on Wigan Road.
During the attack, one of the males sprayed a substance on him, causing serious facial and upper body injuries.
The man was taken to hospital, where he received treatment before being discharged.
Police have launched an investigation into what happened and are appealing for help to find the four people involved.
They want to hear from anyone who saw the four males in the area or have footage of them.
They were described as being white and in their late teens or early 20s. They were wearing dark-coloured sportswear, with one having a distinctive thunderbolt design T-shirt.
Det Con Will Lloyd, of Wigan’s CID, said: “Our investigation has led us to believe that this was a completely unprovoked assault.
“We will not tolerate the use of this level of violence in our communities which is why it is so important we bring those responsible to face justice.
“Anyone with information or images or footage which show a group of males matching this description in the area at the time should share it with us directly or via Crimestoppers.”
Wigan CID can be contacted by calling 0161 856 7094, quoting incident 129 of June 13.
Alternatively, call Crimestoppers, anonymously, on 0800 555 111 or go to crimestoppers-uk.org