The Irishman, 27, fell awkwardly in the Tigers' 2-0 defeat to Eintracht Braunschweig before leaving the stadium heavily strapped and limping, according to the Hull Daily Mail.
Manager Steve Bruce said: "It looks a bad one on first impressions so I wouldn't have thought he'll be fit for Chelsea, which is the big blow.
"Up until now we'd had a few knocks and a few strains but nothing that will keep anyone out for long, so it's a big blow to lose Quinny. He got his foot caught and pulled his hamstring."
Hull are back in the Premier League after three seasons in the Championship.