Police were scrambled to the High Street bar around 1am on Sunday - where a 45-year-old man was found with serious injuries and was taken to hospital.
The injured man remains in hospital and his current condition is not yet known.
Photos taken at the scene the following day showed a large police cordon in place around the popular night spot.
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Detectives are appealing for witnesses to come forward with information about what happened during the attack.
A police spokesman said: “Anyone with information about this incident who has private CCTV installed in the area or who was driving nearby with dash cam installed is asked to contact Detective Constable Jane Cyples quoting reference number 2*369669.”
Any footage which may be of use to officers should be downloaded to a separate, secure device ready for them to view.
You can contact police in the following ways:
Facebook – send a private message to /DerbyshireConstabulary Twitter – direct message the contact centre on @DerPolContact Website – complete the online contact form www.derbyshire.police.uk/Contact-Us. Phone – call 101.
You can also anonymously contact the independent charity Crimestoppers on 0800 555 111 or by visiting www.crimestoppers-uk.org