A 22-year-old suffered head injuries when he was attacked with a glass bottle.
The assault happened in the Slug and Lettuce in High Street, Harpenden, on August 4 between around 1.15am and 1.30am.
Three men aged in their 20s were arrested in connection with the investigation and have been released while enquiries continue.
Police officers have released a CCTV image of a man they would like to speak to in connection with the assault.
Detective Constable Ayodeji Afolabi said: “We believe that the man pictured may have been in the area at the time and could have information that will help the investigation.
“I appreciate the images are not of the highest quality, but if you recognise this man by his facial hair or top, please do get in touch.
“Anyone who recognises the man, or has any other information about the alleged assault, should contact me on the non-emergency number 101, or by emailing ayodeji.afolabi@herts.pnn.police.uk. Please remember to quote crime reference 41/24076/18.”
You can also report information online at https://www.herts.police.uk/Report.
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