Scunthorpe weigh up extending loan for Man Utd keeper Johnstone
The United keeper has impressed for the Iron this season but has missed their last three matches with a broken finger.
Knill said: "His loan is up this week, so we have a decision to make about whether to extend it or not. The first thing we've got to do is make sure he's fit though. He hurt his finger again in training so we're leaving it until this week to make a decision."