Smith won the Scottish Premier League title with Rangers again this season and Fergie believes the title has confirmed Smith as a Scottish managerial great.
Fergie told The Daily Record: “First of all, you need to have ability and endurance to last such a long time as a manager.
“Even more so given the fact that he has had to manage Rangers with the unbelievable expectation and with pressures on him all the time.
“These are things that Walter has always had.
“He has ability, has always been a great coach and, when he reverted to management, he proved the step up was at the right time in his career.
“Walter has gone on to prove himself as one of the best managers in Scottish history.
“The number of trophies he has got, which I think is now 19, tells you that.”
Sir Alex added: “The most important thing is that Walter has always kept his feet on the ground.
“He has always had a great love of the game and never lost that.
“These are the qualities that you need to be successful.”
