Manchester United fans didn’t really know what to make of Cristiano Ronaldo when he first arrived from Sporting Lisbon for £12.2 million.

The skinny 18-year-old was relatively unknown but came with a growing reputation as one of the hottest prospects in Europe.

And it didn’t take long for him to make his mark.

He made his debut against Bolton in August 2003 and his 29-minute cameo showed United fans exactly what they could expect for the coming years.

United were winning 1-0 when Ronaldo was introduced. It finished 4-0 and the Portuguese superstar had terrorised the opposition.

Watch: Ronaldo's highlights from his Man Utd debut

Check out Ronaldo’s highlights from that match:

Alex Ferguson's reaction

After the match, Alex Ferguson couldn’t quite believe what he had just seen.

"It looks like the fans have a new hero," said Ferguson.

“It was a marvellous debut, almost unbelievable. I felt his penetration could make a difference for us.”

But it wasn’t just the manager that Ronaldo had purring.

George Best's reaction to Cristiano Ronaldo's debut

We’ve discovered an interview with the legendary George Best who talks in detail about Ronaldo’s first appearance in a United shirt.

Best was considered the greatest winger United have ever had - until the likes of Ryan Giggs and Ronaldo came along - scoring 181 goals in 474 appearances during his 11 seasons at Old Trafford. He also won two league titles and a European Cup.

And to say that he was impressed with the youngster would be an understatement.

“Cristiano Ronaldo’s first United game as a substitute in the season opener against Bolton was undoubtedly the most exciting debut performance I’ve ever seen,” Best said shortly after Ronaldo’s debut.

“A few of my old team-mates were at the game and they compared him to me.

“There have been a few players described as ‘the new George Best’ over the years, but this is the first time it’s been a compliment to me.

“There have been players who have some similarities, but this lad’s got more than anyone else, especially as he is genuinely two-footed. He can play on either wing, beat players with ease and put in dangerous crosses with his left or right peg. When was the last time you saw that? With Ronaldo and Giggsy on the pitch at the same time, opposition defenders will be petrified!

“Another thing I liked about Ronaldo against Bolton was how he dealt with the physical side. As soon as he came on, he was clattered from behind but he just got up and got on with the game, it didn’t faze him at all. That’s the right attitude. I used to relish it when defenders were trying to kick me up in the air – it only made me more determined to take the p*ss out of them!

“£12.4 million seems a high price for an 18-year old, but I think it’s a snip. You are talking about a lad who, if he stays injury-free, has 15 years ahead of him in the game.

“He’s special, I could see that immediately. In the next few months, thousands of kids will be wearing ‘Ronaldo 7’ shirts and asking their parents to get their hair tinted like him.”

Check out the full interview here.

Sadly, Best died just two years later and he wasn’t able to see Ronaldo fulfil his potential and become the greatest player in world football - winning four (soon to be five) Ballon d’Ors.

But the legendary Northern Irishman knew back then that Ronaldo was destined for greatness.

After all, it takes one to know one.