Dubliner Jonny Hayes will be playing with Celtic from next season.
Aberdeen have accepted a bid of just over £1 million for the midfielder. Hayes scored 9 goals in 32 Scottish Premiership appearances for the club last season.
They finished second behind Celtic last season.
Hayes joined the club from Inverness in 2012, making nearly 200 appearances and scoring 30 goals for the Dons.
Cardiff City were also chasing the midfielder but manager Neil Warnock admitted they had given up the persuit:
"You can only wait for so long and you've got to move on." He told the BBC.
"Aberdeen want two players from Celtic and they've been messing us around for quite a few weeks now.
"And it wouldn't surprise me if their manager Derek McInnes goes to Sunderland either - there might be other motives behind everything stalling.
"We've moved on and gone on to another one or two targets that haven't been mentioned yet."
He's not the only one set to leave Pittodrie
Sunderland have been given permission to speak with Aberdeen manager Derek McInnes.
The clubs have agreed a compensation package believed to be in the 1-million pounds region.