Knill's decisions on those players whose current deals come to an end in the summer had been made ahead of Saturday's final match of the season, which saw the Iron draw 1-1 at Tranmere.
With the numbers of those out of contract stretching into double figures - and including first-team stalwarts like Cliff Byrne, Sam Togwell, Eddie Nolan, Michael O'Connor and Garry Thompson - there is the potential for big change ahead of next season.
"We're speaking to players in contract and out of contract on Tuesday," Knill revealed after the game at Prenton Park. "We've got to make some decisions and some tough ones at that. It's probably the worst part of the job, but you have to make a decision, stick with it and move on. We've already decided and it's going to be a difficult Tuesday."
Knill added: "I am glad the season is over that we can get to grips with what needs to be done over the summer. I'm pleased though that I think we've progressed.
"Obviously we have to make some good signings and bring in some decent recruits that will help what we've got, but I think we're going to get better. Hopefully we'll surprise people next year."