The Republic of Ireland defender was carried off on a stretcher 12 minutes into their 1-0 defeat at the KC Stadium following a collision between himself, Rickie Lambert and Allan McGregor.
While Bruce confirmed there was no break visible from the X-rays, McShane looks set for an injury lay-off regardless.
"We have seen the X-rays and they revealed that there is no break, but I don't know if you have seen it like I have," Bruce said.
"The video evidence doesn't look great, his ankle was in a horrible position so we fear ligament damage. Until we see the scans tomorrow we are unsure but it doesn't look good," he said.
"We now have to just dust ourselves off and get ready for our cup game at the weekend."
Returning to the game, Bruce described Southampton as an "excellent" side after seeing his team drop down to 13th in the table, just three points above the relegation zone.
Bruce conceded that Southampton were by far the better team in a game where his men rarely threatened to score.
"Southampton are the best of the so called smaller teams," he added. "If you take away the big boys then they are the best team and they made life very difficult for us.
"The best team on the night won, we had to be at our best and we weren't. We surrendered possession and went back to front far too quickly, which is not like us. Fair play to Southampton, they put us under pressure in the midfield areas and they were excellent.
"Sometimes you just have to hold your hands up and say you were beaten by the better team."
