Cristiano Ronaldo: Sir Alex Ferguson 'Main Key' to Returning to Manchester United

Cristiano Ronaldo credited former Manchester United manager Sir Alex Ferguson for the inspiration to rejoin the Red Devils on a transfer from Juventus, which became official Tuesday.

Ronaldo spoke with Stewart Gardner of the club's official website on Wednesday about the importance of Ferguson, who retired in 2013 after 27 years leading the side:

"As everybody knows, since I signed for Manchester [United] at 18, Sir Alex Ferguson was the key. I remember when we played against Manchester when I was at Sporting Lisbon. For me, Sir Alex Ferguson is like a father in football for me. He helped me a lot, he taught me many things, and in my opinion of course he had a big role because the relationship that we had, we keep in touch all the time, and he's an unbelievable person. I really like him a lot and he was the main key for me to be in the position that I am, that I signed for Manchester United."

Ronaldo hinted toward Ferguson's importance in his Instagram post confirming the move Tuesday, writing: "Sir Alex, this one is for you..."

The 36-year-old Portugal international arrived to United in 2003 as a player with plenty of potential after scoring just three goals in 25 appearances in his first season as a top-flight player at Sporting CP.

Working alongside Ferguson, Ronaldo transformed into a global sensation at United. He scored 118 goals in 292 matches across all competitions with the club, including a 42-goal campaign in 2007-08 that provided a glimpse of what was going to come at the peak of his career.

In 2015, Ferguson told BBC Sport he felt his former player held the edge over fellow superstar Lionel Messi because of his unmatched goal-scoring ability:

"People say 'who is the best player in the world' and plenty of people quite rightly say Messi. You can't dispute that opinion. But the thing about Ronaldo...Ronaldo could play for Millwall, Queens Park Rangers, Doncaster Rovers or anyone and score a hat-trick in a game. I'm not sure Messi could do it."

He left Old Trafford in 2009 for a nine-year stay with Real Madrid followed by three seasons with Juventus before returning to United.

Ronaldo is with the Portugal national team for a three-match international break starting with Wednesday's World Cup qualifier against the Republic of Ireland. The forward told Gardner he's excited for his first match back in front of the United faithful, though:

"Well, the fans is the key of football. Now, with all the stadiums full of supporters, it's not the same that we had one year ago, those empty stadiums. The fans, they are the key, and I'm so glad. The Manchester United fans, they are special, I know, I remember very well. I know they still sing my music which has made me feel even more happy and my commitment is to give everything on the pitch, like I did before, like I do it all the time, and try to do my best, help the team score goals, make assists, win games, and I hope to see them very, very soon."

His first chance to make his return to the Old Trafford pitch will come Sept. 11 when United host Newcastle United in Premier League action.

The Red Devils are off to a promising start with two wins and a draw through their first three matches. The addition of Ronaldo could provide a spark as the club attempts to win its first Premier League title since 2012-13.