The deal would see Nyatanga moving to Sunderland permanently and Jon Stead who enjoyed a loan-spell at Derby making the move to Pride Park permanent. A straight-swap deal for the Welsh international defender is likely.
Keane said: "Lewin's gone back, there's no update from that. We're going to look at the situation.
"I think he has done well, I thought he did well against Leicester on Monday, in his preferred.
"With the injuries we had, he had to go in and do a job at left-back and he did well. In terms of attitude and everything else, he was top-class.
"We will be monitoring the situation. When players come to Sunderland, mentally they have to be tough because expectations are so high, it's a big club.
"You could say we threw him in at the deep end but I thought he coped very well with it."