Speaking after the Wasps game, Connacht head coach Pat Lam explained: "Gavin caught a boot on the cheekbone at training, so he has a slight fracture there which is a big loss for us."
Mayo native Duffy had to battle a niggling hamstring injury last season and also found himself on the wing at times due to youngster Robbie Henshaw's impressive form at full-back.
Henshaw made his senior debut for Ireland during their summer tour of the USA and Canada and will be hoping to build on his exciting first season at this level.
Connacht have played two pre-season fixtures to date with Duffy, Tiernan O'Halloran and Shane Layden all seeing game-time in the full-back position in the losses to Castres Olympique and Wasps.
The Connacht squad returned to training yesterday. Having used a total of 40 players against Castres and Wasps, Lam will now select a squad of 26 to travel to Newcastle for next Saturday's friendly at Kingston Park (kick-off 3pm).
Back rower Mata Fifita suffered an injury to his AC joint against Wasps and could be out of action for up to four weeks, while David Nolan, David McSharry and Kyle Tonetti continue to make progress with their more significant long-term injuries.
Season Tickets remain the only way to guarantee entry to Connacht's three home Heineken Cup pool matches and 11 RaboDirect PRO12 games.
The province's Season Tickets are still available and can be purchased online at www.tickets.ie or direct from the Connacht Rugby offices in Galway.