Police and ambulance were called to the incident at 2.14pm today, near to Today's Local store.
A cordon has been put in place outside the store while police conduct forensic investigations.
A resident of nearby Coldcotes Avenue said: "I saw guys on a little motorbike. They came down Harehills Lane.
"There was a guy sitting down in front of the shop. Something happened there but I didn't see, then the motorbike sped off."
Police have also cordoned off an area outside Asda Supermarket further down Harehills Lane while they investigate the same incident.
Asda staff have told shoppers that the man ran into the store after the attack and staff grabbed water bottles before pouring them onto him. Empty water bottles can be seen inside the police cordon.
The man is not believed to have suffered any serious injuries.
Detective Inspector James Entwistle, of Leeds District CID, said: “Our enquiries are at a very early stage and we would like to hear from anyone who witnessed any part of the incident or who has any information that could assist the investigation.”
Anyone with information is asked to contact Leeds District CID via 101 quoting log number 992 of October 8.