A woman was hit with a bottle in a bar in Buxton last Saturday following an argument.
The 21-year-old was with a group of friends at The Vault, on High Street, when an altercation broke out with a second group.
She was struck to the forehead with a bottle by an unseen offender, which left a deep cut and needed medical treatment.
A 21-year-old woman has been arrested in connection with the incident, which happened at about 12.45am, and has been bailed pending further inquiries.
Police are appealing for witnesses and want to hear from anyone who saw the incident.
Anyone with information should call Derbyshire Police on 101 or Crimestoppers, anonymously, on 0800 555 111.