Officers say the 30-year-old victim was punched to the ground and had his mobile phone and headphones stolen as he walked home after a night out in Preston.
The incident happened at around 11.45pm on Friday July 17 as the man walked through Avenham Park.
He was approached by two men and was punched to the head and body, causing him to fall to the ground.
One of the men stole his Samsung mobile phone from his pocket and some red Sony headphones that he was wearing at the time. They then ran off through the park.
The first offender is described as white, between 5ft 7in and 5ft 9in tall, aged around 18 to 20 years old, slim build and was wearing a dark coloured hooded jacket and a black and white bandana.
The second offender is described as white, slightly taller than the first offender, also aged around 18 to 20 years old and of a slim build. He was wearing a dark hooded jacket and a bandana.
DC Stephen Gilmore of Preston CID said: “We are keen to hear from anyone who may have witnessed this incident or who was in the area at the time and may have seen two men matching these descriptions.
“It is possible that there might have also been a car nearby around the time of the attack and we would urge the driver of this car to come forward with any information they have.”
Anyone with information can contact police on 101 quoting crime reference SA1608015.
Alternatively Crimestoppers can be contacted anonymously on 0800 555 111 or online at Crimestoppers-uk.org.