The Red Devils are yet to win either competition since Ferguson's retirement at the end of the 2012-13 season, despite a range of managers including Erik ten Hag and David Moyes taking charge.
United slumped to 15th last season, their worst-ever Premier League campaign and despite having no European football this season, Amorim’s side are still struggling in 6th.
Speaking to Press Box, Ferguson has suggested that Amorim will need a decade of rebuilding to construct a side worthy of winning the Premier League once again.
"He is a good personality. It is not easy.
"I remember looking back on my own time there, starting off when Liverpool were the bee's knees. They were a fantastic club, winning the European Cup four times and all that, but then it took them 31 years to win the league again.
"We are now in the same situation. So it could be ten years, could be 11 years, because of that cycle. It has to be thought out carefully, and we have to make sure the recruitment is going to be better than what it was."
Ferguson won the Premier League title 13 times with United and knows what it takes to win the league. United have shown signs of improvement this season, but they are far, far off a side who can compete for the iconic trophy in what may be a several year mission.