Knies should play if he is cleared. His absence has been so noticeable. Hard to believe that he has made that level of an impact this early on into his career, but there has been a very clear void without him in the lineup.
That said, he needs to be 1000000% fully cleared. Zero trace of symptoms. Returning to play this round at the risk of his long term health is absolutely not worth it AT ALL. He is way too big of a piece for our future to be rushing him back into the lineup.
But I do trust the Leafs medical staff to make the right call on that.