Manager Gordon Strachan had been optimistic complete rest since facing Motherwell 10 days ago would have allowed Naka to face the Portuguese.

But, following a second series of scans on his damaged ligaments on the outside of his left knee an injury which has been troubling him since the Champions League qualifier against Spartak Moscow back in August the full extent of the problem has become clearer.

Vital though it is to take all three points against Benfica, Celtic are not prepared to risk further damage to one of their key players.