The Bees today announced their retained and released list, with Donaldson the only out-of-contract player to be offered a new deal.
"When we first spoke to him about a new contract earlier in the season he said he wanted to play in the Championship and ideally that would be with Brentford," Warburton told the club website.
"I have spoken to him and conversations have been positive."
Warburton also wants to bring back three of the club's loan players - Alan Judge, George Saville and Marcello Trotta, from Blackburn Rovers, Chelsea and Fulham respectively - for next season's Championship campaign.
"We are talking to their parent clubs to see if business can be done," added Warburton.
The Bees achieved promotion to the second tier by finishing second in League One, nine points adrift of champions Wolverhampton Wanderers and eight clear of third-placed Leyton Orient.