The man was walking along the pavement of Queen Street near to the pedestrian crossing at the junction with Manchester Road when he passed by two men at around 3pm on Tuesday, March 7, say police
It is believed that one of the men then struck the victim over the back of his head with a bottle leaving him with a two inch cut, they added.
A 19-year-old man from Preston was later arrested on suspicion of wounding. He has been released on police bail pending further enquiries.
A second man is described by police as white, of skinny build, wearing a grey jumper and blue jeans. He was around 5ft 3in and had short hair.
Det Sgt Jerry Sturgess, of Preston CID, said: “This was an unprovoked and callous attack on a defenceless individual.
“The offenders have approached the victim before carrying out a cowardly assault from behind.
“I urge anyone with any information at all to come forward. We are particularly keen to identify this second male.”
Anyone with information about the incident or about the offenders can contact police on 101 quoting log reference 0852 of 7th March.
Alternatively, they can contact Crimestoppers anonymously on 0800 555 111 or online at Crimestoppers-uk.org. No personal details are taken, information is not traced or recorded and you will not go to court.
Anyone with information can contact Lancashire Police on 101 quoting log 852 of March 7th..
Alternatively the independent charity Crimestoppers can be contacted anonymously on 0800 555 111 or online at crimestoppers-uk.org.