The URC match takes place at MacHale Park
Connacht Rugby has confirmed the province's interprovincial derby against Munster in Castlebar in March is a sell-out.
Over 25,000 tickets have been sold for the URC match, which will take place at MacHale Park.
Connacht's previous attendance record is 9,120, set at a Champions Cup fixture in 2011.
The game, which takes place on March 29th, is eight days before Mayo play Sligo in the Connacht football championship at the same venue.