Riordan has a quad muscle injury, while fellow backs John Hearty (hip) and Keith Matthews (rib) and prop John Lyne (calf) are also ruled out.
Both David Gannon and John Fogarty have passed fitness tests this week and the pair have been included on a replacements bench that also includes Matt Mostyn for the first time since last November, after overcoming ankle and calf injuries.
This is Connacht's final Magners League match at home before the new year and coach Bradley is eager to put the record straight after last weeks game against Ulster.
CONNACHT (v Glasgow Warriors): Gavin Duffy; Aidan Wynne, Darren Yapp, Mel Deane, Ofisa Treviranus; Andy Dunne, Conor O'Loughlin; Brett Wilkinson, Adrian Flavin, Robbie Morris, Michael Swift, Andrew Farley (capt), Michael McCarthy, Johnny O'Connor, John Muldoon.
Replacements: John Fogarty, Ronan Loughney, David Gannon, Ray Ofisa, Conor McPhillips, Tim Donnelly, Matt Mostyn.