The Republic of Ireland international could miss out on the forthcoming friendly game against Serbia depending on the extent of the damage
McShane sustained an injury to his left ankle against the Saints and, while initial X-ray scans reported no fracture, club medical staff have advised that further tests should be conducted when swelling reduces.
"He's had X-rays which have revealed no break but the video evidence doesn't look great," Hull City boss Steve Bruce told reporters.
"His ankle is in a horrible position. We fear ligament damage, which we know can be worse than a break."
The injury comes as a blow to McShane, with Republic of Ireland boss Martin O'Neill set to name his squad for the forthcoming international friendly game against Serbia next week.
Meanwhile, Richard Dunne has urged Queens Park Rangers to "bounce back" after suffering a 1-0 defeat away to Championship promotion rivals Derby County at the start of the week.
"We have to bounce back now," Dunne told the club's official website. "We've had two tough games against Burnley and Derby and now we've got another one at home to Reading [on Sunday].
"We've not done ourselves justice over the last week or so, so we need to make sure we get the full three points on Sunday.
"Reading are a good side and will give it everything, but we need to stop worrying too much about the opposition and focus on what we're doing."