Ferguson admits he had "big problem" with Ronaldo's Man Utd debut

Sir Alex Ferguson concedes Cristiano Ronaldo's excellent debut cameo back in 2003 gave him a "big problem".

The then teenage sensation had joined the Red Devils from Sporting Lisbon for just over £12m.

Ronaldo came off the bench in a 4-0 win over Bolton Wanderers at Old Trafford and immediately introduced the crowd to what would become his trademark stepovers.

The Portuguese star joined a team that had dominated English football for the past decade and were defending champions.

Ferguson benefitted from having an immensely competitive squad, but immediately knew it would be hard to leave Ronaldo out going forward.

He said: "With any boy coming from another country, at 18 I think he was the youngest that we ever did that with.

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"So with Cristiano, his mother stayed for quite a bit. I think having a family when you make a move like that, coming to another country, is really important.

"I know that his mother was used to the move they made from Madeira over to Lisbon when he was a young kid. But coming to another country where the language is different, it's a big step for a young person. I think the club did really well.

"I'll always remember that when we had the discussion, I think what I wanted to impress upon his agent, in particular, was that he won't play every game, but if he's so good I can't stop him. You always play your best players.

"For the opening game of the season he was a substitute, came on and was absolutely fantastic. The crowd was magnificent. The crowd loved it.

"Here we had a situation. Do I play him the next game? Or do I put him back on the bench? That's a big problem, that."

Ronaldo did start on the bench in the season's second game at Newcastle United, coming on for the final 13 minutes.

His first goal for the Red Devils came in November as Ferguson's side beat Portsmouth 3-0.

The Portugal star endured an impressive start to life in Manchester, but was far from prolific.

Upon returning from the World Cup in 2006 he was a man reborn however and transformed into the free-scoring player we know today.

During his initial stint at Old Trafford Ronaldo won three Premier League titles and the Champions League, which resulted in him winning the first of his five Ballon d'Ors in 2008.

Ronaldo return to United this summer, citing Ferguson's influence as a factor.