Sir Alex Ferguson has described Arsene Wenger as "one of the greatest Premier League managers", adding: "I am proud to have been a rival, a colleague and a friend to such a great man."
"I am really happy for Arsene Wenger," he said.
"I have great respect for him and for the job he has done at Arsenal. It is great testament to his talent, professionalism and determination that he has been able to dedicate 22 years of his life to a job that he loves.
"In an era where football managers sometimes only last one or two seasons, it shows what an achievement it is to serve that length of time at a club the size of Arsenal.
"I am pleased that he has announced he is leaving at this stage of the season, as he can now have the send-off that he truly deserves.
"He is, without doubt, one of the greatest Premier League managers and I am proud to have been a rival, a colleague and a friend to such a great man."