Donaldson has scored 10 goals this season for the Bees, but only has six months left on his current contract.
Brentford kept hold of the 29-year-old amid interest from League One rivals Wolves in summer, but the fact that he has yet to extend his contract has prompted fears he may be sold in January.
"We've met with his agent several times to see what he's looking for," Warburton said in the Fulham Chronicle.
"Clayton's one of our older players and he's a very ambitious guy. He's got aspirations to play in the Championship, but we want that to be with Brentford.
"Both parties will talk again before Christmas.
"We didn't pay a fee for Clayton. He's provided a great service to the club and has certainly given us value for money. We're looking to keep him.
"If Clayton's enjoying his football and scoring goals he'll be happy, and if he's happy he'll certainly want to stay at Brentford."