It happened in The Oval, Seacroft, at about 1.30pm on May 10.
A man in his thirties was seriously injured after being hit with a hammer in an unprovoked attack.
He was treated in hospital for a broken eye socket and broken jaw after being assaulted by two of three males who approached him on two mopeds.
The suspect who wielded the hammer was wearing an aqua blue helmet and was on a white moped.
Police have released a CCTV image which shows the suspects at a nearby petrol station shortly before the attack.
Anyone who knows the man with the distinct helmet, or who has any information on the attack, is asked to contact the police.
Contact DC 3198 Ellis at Leeds District CID via 101 quoting crime reference 13220251006, or online via the Live Chat.
Information can be given anonymously to the independent charity Crimestoppers on 0800 555 111