"We have conceded too many goals not just from headers and that's surprising as we have good defenders, it's a matter of concentration and work on the training ground. Defenders have to work hard on defending in training and perhaps with all the games we have had in September, that might not have been done.
"I wasn't happy with the manner in which we lost last week so we will have to make sure we do something about that."
One player who will not be risked is Dave Hibbert who is still suffering with the nose injury, however Delroy Facey may make the squad but the game may be to early for him to feature in the game.
Speaking about Hibbert to the Rotherham Star, Knill said: "If he gets a knock in the face, he has to stop - it affects his breathing. He missed last weeks game, but trained all this week. Hopefully, this will have helped him, but we are wary,"
Full team news plus head to head will appear on the site for both Vale and the Millers later tonight.