The 35-year-old Celtic captain has been tipped to move to Aberdeen to work with new boss Stephen Glass as his assistant and also prolong his playing career.
It has been claimed that he has held talks with Aberdeen chairman Dave Cormack and has already verbally agreed to the move to the Dons while deciding to end his 14-year stint with Celtic.
Donnelly stressed that it would be a massive loss for Celtic, especially ahead of next season, where his experience could be vital in a period of upheaval under a new management team.
The former Bhoy wants Brown to stick around for at least one more year, but conceded given his service to Celtic he reserves the right to make the decision to leave the club when he wants.
The former Celtic star said on the Celtic Huddle Podcast: “[It would be a] huge loss.
“I think for the new management team coming in here and transitioning in a period of Celtic’s history where there is going to be a lot of coming and going, somebody of his leadership is going to be so important at the club.
“On the pitch, off the pitch everything to do with it.
“I think it will be a huge loss if he goes.
“He deserves the right to make that decision.
“He has achieved so much at Celtic and if he decides to go I wish him well, but I would really like him to stay another year.”
Brown has won ten league titles, six Scottish Cups and seven Scottish League Cups during his time at Celtic.
