Alex Sandro living up to his billing as 'new Roberto Carlos' at Juventus

Porto are renowned experts at selling players at hefty prices, but not all of those stars proved to be successful in new surroundings.

Manchester City fans still don't understand why Eliaquim Mangala -- who cost the Premier League club £42 million three years ago -- was so highly rated, while the Frenchman is currently struggling on loan at Valencia. Jackson Martinez had a disastrous short spell at Atletico Madrid before Los Colchoneros happily shipped him off to China. Danilo is so error prone that Real Madrid barely give him opportunities after paying €32m for the right-back. Giannelli Imbula became a bench warmer at Stoke City and never justified the monstrous £18m fee.

In fact, Porto would gladly play against any of them these days ... but perhaps not Alex Sandro. On Wednesday, the galloping Brazilian left-back returns to Estadio do Dragao with Juventus for the Champions League round-of-16 clash, and he is a crucial player for the Old Lady. Arguably the least hyped of all recent Porto exports, he definitely is the best of the crop.

It is all about grabbing your chances with both hands, and Alex had done that with some aplomb. Juventus fans were not overly excited when he was signed in August 2015 for €26m, and he was supposed to play second fiddle to Patrice Evra. Coach Massimiliano Allegri wanted to introduce him gradually, but the new recruit had other plans, even when given just a few moments to impress.

You might have forgotten that by now, but Juventus had a disastrous start to the 2015-16 season. With four defeats in their first 10 Serie A fixtures, they arrived to the derby against Torino in 12th place. Their city rivals were actually ahead of them, and the game was drifting to a disappointing 1-1 draw when Alex was introduced with three minutes remaining. He proceeded to provide a sublime assist for Juan Cuadrado's winner in injury time, the champions never looked back, and the crisis was over.

A month later, Alex again entered the field as a substitute and sent in a brilliant cross for Paulo Dybala to score the only goal in the big game against AC Milan. Another four days passed, and he assisted Mario Mandzukic as Juventus defeated Manchester City 1-0 in the Champions League.

It was evident that his contribution could become fundamental for the team, especially as Allegri often used the 3-5-2 formation. Alex is a very attack-minded full-back, who feels liberated and performs even more efficiently as a wing-back. That makes him brilliantly suited for a system with three centre-backs, and Juve didn't hesitate to put him in midfield as well at times.

Such attacking prowess didn't surprise anyone in his homeland, where he started out as a playmaker in his childhood. Only shortly before joining the senior squad at Atletico Paranaense, Alex was advised to move to the flank by the youth coach Marquinhos Santos, who promised that such a switch would pave his way to the national team. The youngster felt a bit uncomfortable in the beginning, but admiring Roberto Carlos most certainly helped. The legendary Brazil left-back was one of the youngster's idols, alongside Ronaldo and Rivaldo, when he followed the 1998 and 2002 World Cup tournaments on TV. Upon getting his new role, Alex tried to emulate him.

Joining attacks as often as possible is only natural in such circumstances, and Alex was duly nicknamed "the new Roberto Carlos" when playing for Santos on loan between 2010 and 2011. Having Neymar, who has remained a friend ever since, as a partner helped in more ways than one -- not only was the country's brightest young star a superb partner on the wing, but he also made life much more difficult on the training ground, leading to constant improvement in Alex's defensive abilities. Taking into consideration that Neymar was not too fond of backtracking, the left-back had to be very disciplined himself, and his progress was clear for all to see.

Alex's time at Santos was memorable as the club won the Copa Libertadores title for the first time in 48 years. Immediately afterwards, in the summer of 2011, the defender was ready to cross the Atlantic. He did so long before Neymar, and joined Porto six months before Danilo made the same move, also from Santos. The club didn't rush things, and Alex spent most of his debut season on the bench, but there were no complaints.

"Porto have a culture of signing new players and gradually training them. That is excellent, because you have to think much faster on the pitch in Europe," Alex said in retrospect.

The following three seasons were highly successful from a personal point of view, and Alex gained invaluable experience in the Champions League before Juventus came calling.

It must have been a huge compliment for the defender when Roberto Carlos himself told Tuttosport: "Alex can be my heir, and I see a bit of myself in him. He is a modern full-back who knows how to defend and to attack. He might not shoot at goal like me, but I have to admit that his crosses might be more precise than mine. That's his specialty, and his balls are very inviting for strikers."

He was most definitely right, as Cuadrado, Dybala and Mandzukic have taken full advantage of those majestic crosses. Alex is extremely quick, able to outpace any defender and send accurate assists with just one touch on a run. That is quite a rare quality, and Allegri was satisfied with Alex's contribution at the back as well. It is only natural that by 2016 he became an integral part of the lineup.

Such was Alex's impact that Evra, whom he initially described as a player to learn from, completely lost his place at Juventus, and eventually opted to move to Marseille last month. Now, at the age of 26, he must be considered a true world-class star.

He has been mentioned as a potential target for Manchester City, who need a new left-back, while Chelsea are possible suitors too -- he would be ideal for Antonio Conte's 3-4-3 formation.

The only problem remains with the national team. Alex made his debut for Brazil back in 2011, but was largely ignored after the London Olympics defeat in 2012. Dunga, who said that a move to Italy should open the door for the defender, called him up a year ago, but didn't use him in a pair of World Cup qualifiers and omitted him from the Copa America Centenario squad. Current coach Tite has put his faith in Real Madrid's Marcelo and Atletico Madrid's Filipe Luis.

Continuing success with Juventus should eventually change that, and a good run in the Champions League this season won't hurt Alex's chances. Porto know only too well how dangerous their former star is, and they will be hard-pressed to find a way to stop him.