Valencia went down after a seemingly innocuous incident involving Kirk Broadfoot and immediately signalled he was in trouble.
TV replays showed his foot pointing in the wrong direction and he was eventually stretchered off, with Broadfoot in obvious distress.
"It is a dislocation or a fracture and he gets operated on tomorrow morning," confirmed Ferguson following the 0-0 draw.
"It was an innocuous challenge but when you saw the Rangers player waving, you knew it was a bad one.
"It is a bad blow for the boy. It is similar to the injury Alan Smith got and you are talking about the rest of the season."