Newcastle manager Eddie Howe says midfielder Jonjo Shelvey is speaking to Nottingham Forest over a January move.
Former England international Shelvey, 30, has made only three Premier League appearances this season and his contract expires in the summer.
Howe said: “I definitely want to keep Jonjo. I rate him very highly.”
But he added that it “would be very difficult to keep Jonjo, with where he wants his career to go”.
Newcastle striker Chris Wood joined Forest on loan this month.
Howe said: “Jonjo has been a huge player for this football club over the last seven years. He has been a very important part of my squad since I’ve been here. Unfortunately, he’s had injuries this season.
“Certainly, I would not want to lose him but, similar to Chris Wood, I have to understand the player’s wishes with his contract coming to an end this summer.
“You can keep players that want to leave, but you have to take every situation independently and try and judge what’s best for him and the club.”
Shelvey has made 202 appearances and scored 18 goals in all competitions since joining Newcastle from Swansea City in 2016.
Newcastle are third in the Premier League and hold a one-goal advantage over Southampton heading into the second leg of the Carabao Cup semi-final on Tuesday.