Out-half Miah Nikora, who had to retire after being dazed by a blow to the head in the opening half against the Blues on Friday, is also doubtful.
Liam Bibo returns to the squad, but Niva Ta'auso and David Nolan remained ruled out through injury.
Connacht coach Michael Bradley hopes to finalise his team on Thursday morning.
CONNACHT Squad (v Ulster): Backs (11) - Liam Bibo, Fionn Carr, Gavin Duffy, Ian Keatley, Keith Matthews, Frank Murphy, Troy Nathan, Miah Nikora, Conor O'Loughlin, Brian Tuohy, Aidan Wynne.
Forwards (13) - Andrew Browne, Sean Cronin, Adrian Flavin, Jamie Hagan, Ronan Loughney, Mike McCarthy, Mike McComish, Robbie Morris, John Muldoon, Johnny O'Connor, Ray Ofisa, Bernie Upton, Brett Wilkinson.