On the southern fringe of Lisbon, across the River Tagus, stands a school for the spectacular. The youth academy of Sporting Clube de Portugal produces sensational attacking talents with the sort of extraordinary frequency that holds a deep fascination for Europe's wealthiest powers.

Manchester United's purchase of Nani last week for an estimated £17m plundered one its latest graduates. The 20-year-old winger is an outstanding prospect, yet he is merely the latest in a phenomenal series of attacking midfielders that began with Luis Figo and encompasses Cristiano Ronaldo, Simao Sabrosa and Ricardo Quaresma.

No other club can claim to mould so many outstanding touchline talents from the raw materials they inherit.

It was once Barcelona who had a direct line to the sales department of Sporting's hierarchy. Figo moved to Camp Nou in 1995, achieving an iconic status which was subsequently reduced to rubble by his decision to join Real Madrid, and Barcelona twice returned to the Portuguese capital in search of potential successors. Simao joined from Sporting in 1999, while Quaresma was recruited three years later. Neither fully lived up to their billing in Catalonia and they returned to enjoy success in Portugal with Benfica and Porto respectively. Yet such was Quaresma's ability that it was he, rather than Ronaldo, who was once regarded as the greatest jewel to be mined from the Sporting system.

Ronaldo has, of course, made a mockery of that prediction since his arrival at Old Trafford. No list of the top three players in the world would now seem complete without mention of the 22-year-old. He had long been vocal about his view that Nani should follow him to Lancashire, and United supporters can now relish witnessing the fruits of the youngster's acceptance. Having the Portuguese double act working in tandem next season presents a frightening prospect to those seeking to depose Sir Alex Ferguson's side as Premiership champions.

Sporting invested more than £8m in developing their academy, which was last year renamed the Academia Puma as part of a sponsorship agreement struck with the sportswear brand. The transfer fees received have been more than enough to balance the books and there are others waiting to boost the bank balance further.

Alongside Nani, Miguel Veloso and Joao Moutinho, both midfielders, and Yannick Djalo, a striker, completed the quartet of 20-year-olds who were regulars during Sporting's thrilling end to the Superliga season. A run of nine wins and a draw in their last 10 matches saw the club pipped by a single point by Porto in the chase for a first title in five seasons.

"Miguel Veloso is a good example of what makes the academy successful," says Thomas Kundert, a Sporting season ticket holder who runs the website Portugoal.net.

"He is the son of a very famous right-back who played for both Benfica and Portugal, and Benfica wanted to sign him when he was about 14 or 15. Instead, he joined Sporting because he knew there would be opportunities in the first team at an earlier stage.

"I think that's just as significant as the excellent scouting system the club obviously has in place. Sporting play far more young players than either Benfica or Porto. Nani was a regular at 18 and that kind of example makes players choose to go there. It's hard to think of any other European club competing for a national title which had four homegrown 20-year-olds in its best XI."

Sporting recruit players from an early age into various programmes around Lisbon, but it is not until they are 12 or 13 that they are brought into the academy to concentrate their development. It was at that stage in life that Ronaldo moved 600 miles from his home in Madeira to join the club, where team-mates initially mocked his provincial accent before becoming increasingly awestruck by his technical talents.

Nani has now followed as the latest golden boy to be sold, creating further debate about the need to balance financial income against Sporting's ambitions to succeed at the highest level.

"Sporting are back in the Champions League next season and the supporters hope a great European run might persuade players to stay for longer," says Kundert. "It would be better to keep players until they were 24 or 25 rather than losing them at such a young age. But these are the economics of football."

Spectacular players guarantee spectacular returns. Sporting are unlikely to reach for the begging bowl any time soon.