Scotland international has grown disillusioned at the club after seeing top players leave and his boss has promised him a move if the side are not in contention for promotion
The 24-year-old has a year left on his current deal and Warnock wants his captain to sign for another term.
The Scotland international has been linked with a move away from the club after a couple of impressive seasons in the Championship and the 63-year-old understands the forward's frustrations at seeing other top players leaving the club.
"I want to keep him. He knows what I think about him," Warnock told BBC Radio Sheffield. "I've said to him to sign another year and, if at Christmas we've no chance of going up, I'll sell you then.
"I understand that he's frustrated because all of the midfielders he was playing alongside last season have left the club.
"I think he's just going to wait and see who we sign and see how the situation develops and I don't blame him for that."
"It's a challenge now to get a squad together that is capable of winning promotion and I want a shot at achieving that" - Neil Warnock
The former Sheffield United boss is also keen to secure the future of Ross McCormack at Elland Road with the Scot's contract set to expire in June.
McCormack was the club's top scorer last season with 19 goals and has been offered a new contract, which has been rejected.
"We've offered him a new contract and it isn't sufficient to what his advisors think he should get," Warnock added.
"That's fine, he got 19 goals for us this season but what we've said is we can't go that far. That doesn't mean he's going to go though."
Warnock is looking to mount a promotion challenge next season after seeing his side fail to reach the play-off positions last season.
"It's not been easy so far, it's a massive club," he added.
"It's a challenge now to get a squad together that is capable of winning promotion and I want a shot at achieving that.
"Only time will tell if I'm going to get the backing that allows me to do that. I'm trying to get one or two players signed up sooner rather than later."