Police are looking for a man who was injured in a group fight on Sunday at the junction of High Street with Portland Street, in front of the One Stop Shop.
The incident took place at about 6.45pm on May 15, and involved three men punching and kicking a male victim on the ground.
The victim left the scene before the police arrived and officers still have not traced or spoken to him.
He walked away towards the city centre with visible injuries to his head and a hand.
Three local male suspects aged 23, 31 and 34 were arrested nearby on suspicion of affray.
They were interviewed and released on police bail to return to the police station after further enquiries have been carried out.
CCTV did show a Cub Scout group walking past the suspects a few minutes after the incident. Police say they may have witnessed something, though it is not thought that there is any footage of the assault.
Anyone with any information is asked to contact PC John Richardson or PC Elizabeth Knight at Lincoln Police Station on 0300 111 0300.