A woman was hit in the face before her partner was struck over the head with a bottle several times during the incident in the early hours of Saturday.
Derbyshire police say the woman sustained a broken jaw and a broken tooth during the assault.
A force spokesperson said: “The incident happened in Corporation Street at around 2.30am on 21 May, when a woman was reportedly hit in the face by a man.
"Her partner then intervened, and the man hit him over the head with a bottle several times, before once again assaulting the woman by punching her in the face.”
A 19-year-old man was arrested on suspicion of GBH and has since been released under investigation, pending further enquiries.
The police spokesperson added: “We are keen to hear from anyone who witnessed the incident, or who might have private CCTV or dashcam footage that has captured what happened.
“Witnesses, or anyone with information, should contact us via the following methods quoting reference 22*289603.”
Facebook – send a private message to the Derbyshire Constabulary Facebook page
Twitter – direct message the force’s contact centre via @DerPolContact
Website – The force has several crime reporting tools on its website or use the online contact form
Phone – call officers on 101.
You can also anonymously contact the independent charity Crimestoppers, on 0800 555 111, or by visiting the Crimestoppers website.