A man suffered two fractures to his jaw following an unprovoked attack in Langley Mill.
The crime happened on a footpath which leads from the A608 Station Road next to St Andrew's Church, past the industrial estate and up towards Laceyfields Road, Heanor.
A 29-year-old man was walking along the path in the Heanor direction when a man walking the other way punched him in the face.
The victim suffered two fractures on the left-hand side of his jaw and needed hospital treatment.
Since the assault - which happened between 8pm and 9pm on September 24 - officers have been carrying out enquiries in the area and now want to issue a wider appeal for witnesses.
A Derbyshire Constabulary spokesman said: "Unfortunately we don't have a description of the offender due to it being dark at the time of the offence.
"If you saw the offence take place or you have any information that could help, call PC Andy Brooks on 101, quoting reference 17000429224.
"You can also call Crimestoppers on 0800 555 111."