Hayes was linked with a move back to Scunthorpe last week, but the Iron have not made an approach to bring him back.
"We heard that he was available but it seems not, so we're not going to pursue it," said Knill, the Iron manager.
"If he becomes available we'll see what we can do about it. As of now Paul himself says he's not going to be coming back."
Brentford have been touted as a likely destination for Hayes, which would avoid the hassle of uprooting his family to move back to North Lincolnshire.
It seems unlikely he will remain with the Addicks this term. He has found himself bolstering their youth team in pre-season, and Powell confirmed on Saturday he is free to leave The Valley along with teammate Leon Clarke.
"They are two players who want to play regularly and I’ve said to them ‘I will find it hard to play both of you regularly’," he said.
"They both want to play and I want to be fair to them that if it isn’t going to happen for them here, whether we can fix up a permanent or loan move for them, that may happen."
Hayes was quick to distance himself with a return to Glanford Park last week, using Twitter to tell fans he would not be back for a third spell in claret and blue.
Two players almost certain to be completing their moves to the Iron are Irish pair Mark Hughes and Jordan Keegan.
They have agreed contracts to join, and their transfers are only being held up by "red tape" as they last played in the Republic of Ireland.