Sussex Police said officers attended the Admiral Steps on Nelson Road around 11pm on October 9, 2020 following reports a man had been stabbed in the leg.
He was treated at hospital before being discharged to recover at home, police said.
A spokesperson added: "Extensive enquiries have taken place since the assault, and officers have now released an image of a man they would like to speak to in relation to the matter.
"Anyone who recognises him, or who has any other information about what happened, is asked to contact police online or by calling 101 quoting serial 47200174426.
"Alternatively, you can contact the independent charity Crimestoppers anonymously on 0800 555 111."