#3 Jaap Stam
During Sir Alex Ferguson's era at Manchester United, Jaap Stam was one of the finest defenders. The Dutch defender was signed from PSV Eindhoven for a fee of £10.6 million in 1998, becoming the most expensive defender back then.
The tall centre-back was signed by Alex Ferguson to stabilize the United defense and his impact was seen immediately. With his strong and tall physique, quick pace and ball-playing abilities, Stam had an authoritative presence at the back.
He played an instrumental role in securing the treble in the 1998-99 season. During his time at Manchester United, Stam won three Premier League titles, the FA Cup once and the UEFA Champions League once.
In his autobiography, Stam allegedly expressed his views on opposing players and accused Alex Ferguson's approach of signing him without the consent of PSV. This did not bode down well with the Scottish manager. Stam was eventually sold to Lazio in the 2001-02 season, ending his stint with the Red Devils.
In 2007, Alex Ferguson admitted that selling Stam was one of his mistakes back then. He was of the opinion that he and his team misjudged Stam's performing capacity after he returned from an achilles injury.
#2 Paul Pogba
Paul Pogba is one of the most talented midfielders in the world right now. The Frenchman graduated from Manchester United's academy and was touted to become one of the best midfielders during his youth days with the Red Devils.
Initially, even Alex Ferguson highly regarded Pogba's capabilities. But somehow the Frenchman did not get enough chances at United even when first-choice midfielders were not available. In an interview last year, Pogba stated Alex Ferguson did not trust him in those times.
In 2012, after not signing a new contract, it was confirmed that the French midfielder had joined Juventus. Alex Ferguson then accused Pogba of being disrespectful to the club. Paul Scholes had retired back then and United could have really benefited from the Frenchman's availability.
Pogba went on to become a massive sensation at Juventus. He has scored 28 goals and assisted in 36 others in his 124 appearances in Serie A. It was more than about his goal contributions in Turin. Pogba, with his strength, technical and passing abilities, was at times unstoppable in midfield.
He attracted a lot of interest from top European clubs during his time with the Italian giants but United were successful in bringing back the Frenchman. Manchester United re-signed Pogba in the summer of 2016, for a hefty fee of £89.30 million. Had Alex Ferguson kept the Frenchman back in 2012, Manchester United could've possibly saved the hefty transfer fee.
#1 Cristiano Ronaldo
Cristiano Ronaldo impressed Alex Ferguson during his Sporting Lisbon days, especially when Manchester United faced them in August 2003. The Scotsman wasted no time in pushing to sign the young Portuguese back then.
Ronaldo signed for Manchester United in the summer of 2003 and went on to become one of the best players in the world. The forward was a beast of a player for the Red Devils during his first stint. His dribbling skills, combined with pace and goal-scoring abilities, created havoc in the opposition defense.
He played 196 matches in the Premier League in his first stint, scoring 84 goals and recording 34 assists in the process. The former Sporting winger went on to win the Ballon d'Or in 2008 whilst at United. He won three Premier League titles, one FA Cup, one UEFA Champions League and the FIFA Club World Cup once with the Red Devils.
Alex Ferguson was like a father figure to Cristiano Ronaldo. The Portuguese, after having spent six seasons at United, wanted to join Real Madrid in 2009. Alex Ferguson did not get in his way and allowed the dashing winger to join Los Blancos for a then world record transfer fee of £80 million.
There was very little Alex Ferguson could do at that moment. After leaving Manchester United, Cristiano Ronaldo went on to achieve an incredible amount of success with Real Madrid. In the process, he added four more Ballon d'Or awards to his collection.
It would have been lovely had the Portuguese not left back then. In those 12 years away from Manchester United, the former Real Madrid forward has matured into a more experienced and successful player. Ronaldo has now finally returned to Old Trafford this summer and has already scored four goals in three games across all competitions.