The winger had to be stretchered from the field and straight to hospital after picking up an ankle injury from an innocuous-looking challenge from Kirk Broadfoot in the second half of the game against Rangers.
Ferguson told Sky Sports: "He has gone to hospital. It looks as if it is a dislocation and a fracture.
"It's a bad one, it will keep him out for a long time. He seemed to dig his toe in the turf."