"Richard has been outstanding for Manchester City. He is the ultimate professional and has served the club magnificently. Winning the player of the year award for four consecutive years tells you everything about him. We all wish him well for his future career at Aston Villa," he told City's website.
"It would have been difficult for Dunney to stay given his standing at the club and I understand that. I wasn't going to stand in his way. I could have tried to stop him going and said I wanted him as a squad player but out of respect for what he has done for City I wasn't going to do that.
"Not only has Richard performed exceptionally well for this club over the years but he has been a terrific ambassador and is a inspiring person who commands the respect of everyone. He has conducted himself in a impressive manner throughout my time here and way beyond that."