Officers were called to the scene in Rockley Hall Yard off The Headrow at 9.48pm on Sunday.
The victim - a man in his 50s - had been drinking in the pub when he was approached by the woman offering a Leeds United top for sale.
He followed her down a nearby alleyway, where a man appeared and punched him to the head with such force that he was knocked to the floor.
His wallet containing cash was taken, police said.
The suspects then ran off down The Headrow towards Vicar Lane.
Detectives have now launched an appeal for more information.
The woman was described as white, about 5ft 9ins tall, medium build with darkish hair and has a Leeds accent.
The man was described as white, tall, slim, with short dark hair.
Anyone who witnessed the incident or who has any information that could assist in identifying the suspects is asked to contact PC 3069 Nicholson at Leeds District Crime Team via 101 quoting crime reference 13210560247 or online via www.westyorkshire.police.uk/101livechat
Information can be given anonymously to the independent charity Crimestoppers on 0800 555 111.
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