Blackstock faces around a year out with ligament damage following a tackle by Cardiff midfielder Seyi Olofinjana in the closing stages of Forest`s 2-0 victory in the Welsh capital last weekend.
"It is an horrendous injury. It is going to be 12 months minimum before he is back," said boss Billy Davies.
"I have asked our chief executive to look at the video and make a club decision about what we should do next. We have to decide, as a club, whether we want to complain."