Derek Young, David McNamee and Mark Howard will leave the club at the end of the season as loanees Steven Smith, Nikola Vujadinovic and Nick Blackman return to their parent clubs. Zander Diamond's contract is up at the end of the season and is expected to go to Hearts.
Dons were disappointing in their 2-0 defeat by Saints and asked by RedTV if the uncertainty affected the players, Knox replied: "I think it must do."
Aberdeen manager Craig Brown is also expecting Sone Aluko to return to English football in the summer while Chris Maguire and Jamie Langfield have to make decisions on the contracts that have been offered.
"You are always going on to players that every time they take to the football field they have to perform," added Knox.
"Knowing full well that a few of them might be out next season, it is difficult for them to motivate themselves. That's no excuse on their part but invariably that's what happens, especially in the position we are in.
"We can note the injuries and certainly we have an injury list which is crippling but you are always looking for the right application and St Johnstone were better at that than us."
Ahead of the visit of St Mirren on Tuesday night, Knox added: "Everyone recognises that there is a freshness needed throughout the club. We will endeavour to do that.
"There is only so much you can do but we will be trying to bring in as many players as we possibly can in the positions that are needed.
"But again we have to wait and see if the players offered contracts like Sone and Chris Maguire, are staying here or going but we will know that by the end of the week."
Source: PA
Source: PA