Nemanja Matic's return to Chelsea from Benfica after leaving in 2011 as a makeweight in the David Luiz deal is yet another astonishing piece of business by Portugal's leading clubs. The Serbian midfielder returned to Stamford Bridge for around £21m, a remarkable fee given he was valued near £3m when he left three years ago.

In recent years Ramires, Fábio Coentrão, Ángel Di María, Javi García and Axel Witsel have left the Estádio da Luz for a combined transfer total of around £134m and a profit of more than £100m. It is thought Benfica may yet sell more of their assets in this window, with both their Argentinian centre-back Ezequiel Garay and striker Rodrigo linked with a joint move to Zenit St Petersburg. The former has also been linked with a move to Manchester United for some time.

However, these profits are dwarfed by those made by Benfica's rivals in the north, Porto. Under the stewardship of their shrewd president, Jorge Nuno Pinto da Costa, Porto have not only sold their key on-field assets for large profits but done so without damaging the club's success on the pitch.

Since José Mourinho led Porto to their second Champions League success in 2004, the club have made some €400m profit (£342m) in player sales. Despite the departures of Radamel Falcao, Hulk and, more recently, James Rodríguez and João Moutinho, Porto have continued to dominate the domestic scene, winning seven league titles since 2004. Couple this with four Portuguese Cup triumphs and a Europa League victory and Porto's model seems to contradict those who claim success is built on stability – especially as they have had eight different managers in this period.

In there, somewhere, is a lesson for Premier League clubs.

Porto's scouting network is among the most extensive in world football. Their director, Antonio Henrique, says: "We work with 250 scouts around the world in countries that make sense for football because we will not send anyone to Bangladesh. We have internal and external scouts, who are divided into several levels of observation, which allows a player to be viewed by several people. They work with a shadow team, which is a set of players who are identified from various leagues and capable of being hired by Porto."

Whereas Benfica and Porto focus on importing their talent, Sporting's model is focused on nurturing their own talent at their excellent academy in Alcochete, a 40-minute drive west of Lisbon. It has one of the best production lines in Europe, with stars such as Cristiano Ronaldo, Luís Figo and Paulo Futre progressing through its ranks. Last week the latest talent, 19-year-old Carlos Mane, scored a stunning goal on his full debut against Maritimo.

For a nation that has experienced economic hardship in recent years, its football clubs at least seem to be bucking the trend. The head of the Portuguese league, Manuel Figueiredo, said last year that between 2001 and 2011 Portugal was the only European Union country with a positive net balance in player trade, with sales of some €1 bn euros and a €400m surplus. "The secret for a small country like us to stay up there with the very best is to be highly professional and nurture talent," said Figueiredo.

"This happens all throughout the value chain, not just with Porto and Benfica but also with clubs like Braga and Maritimo and in the lower leagues."

Portugal offers a gateway into Europe for many young South Americans, with Brazilians, in particular, profiting from the lack of a language barrier. The nation's more relaxed approach to immigration and the relative ease it offers in obtaining an EU passport makes Portugal the ideal stepping stone.

Da Costa says Porto have to keep their eye on the ball to remain competitive: "We have to be permanently studying the youth market. This is what allows us to keep fighting, despite having a budget 20 times less in respect to income than others. Players come here and feel at home straight away."

Porto and Benfica, despite their stature, are nowhere near able to compete with Europe's giants due to the lack of income from television rights. In 2012-13 Porto received €13.2m in television money following their championship-winning campaign. Manchester United received £60.8m. Queens Park Rangers finished bottom of the Premier League last season but still received a TV fee of £39.8m, dwarfing that of Porto.

Portuguese clubs may have had their hand forced in the transfer market but they have subsequently developed a remarkably successful business model. With the introduction of financial fair play this season, it may yet become the blueprint for many European clubs.