Ferguson joined the floods of tributes being paid to former England captain and manager Keegan, who enjoyed a stellar playing career which involved spells at Scunthorpe United, Liverpool, Hamburg, Southampton and Newcastle.
He claimed three league titles, the European Cup, two Uefa Cups and the FA Cup during a six-year spell from 1971 to 1977 at Liverpool.
He helped Hamburg win the Bundesliga and earned back-to-back Ballons d’Or in 1978 and 1979. Keegan remains one of only four English players to have won the award to date.
As a manager, he was also in charge at Fulham and Manchester City in addition to England and Newcastle.
Keegan signed Alan Shearer for a world record £15m fee for Newcastle in 1996 and also took charge of England at a time when the striker was captaining his country.
“He was my friend. A man everyone loved. For his passion. For his energy but most of all for his friendship. He loved football and he loved Newcastle more than anything,” said Shearer.
“I’m so honoured to have known him. We will miss you Kevin.”
Newcastle United’s current manager Eddie Howe got in touch with Keegan when he was appointed by the Magpies in 2021.
“Kevin was an inspiration to me as a young player and, I’m honoured to say, a friend whose guidance and support meant a great deal in recent years,” said Howe.
“He showed me incredible warmth and generosity. He had already given so much to this football club, yet he immediately made me feel welcome.
“Kevin understood better than most the privilege and responsibility of leading Newcastle United. He was always willing to share his wisdom, offer encouragement and provide support, and I will always be grateful for that.”
Former Scotland and Liverpool forward Sir Kenny Dalglish described Keegan as “one of the very best players of his generation” who “wore Liverpool’s famous number seven shirt with great distinction”.
“His achievements on the pitch were exceptional, but he was also a wonderful person and genuine gentleman,” added Dalglish, who was signed from Celtic to replace Keegan at Liverpool in 1977, and later also succeeded him as manager of Newcastle.
“He gave so many people wonderful memories and his teams played the game in a way that supporters loved to watch.
“Football has lost one of its true greats.”