Felix became the fourth most expensive footballer in history when Atletico beat off competition from around Europe to pluck the young striker from Benfica after just a single season of top-flight football, although his 15 goals from 21 league starts in the Premeira Liga did indicate they had a truly special talent on their hands.

Life since then has not always been easy in the Spanish capital. "All people need time," said manager Diego Simeone last month when asked what had clicked for his Portuguese prodigy. Felix had performed in fits and starts, a moment here and a moment there, but is now finding true consistency.

That backing came midway through a run of eight straight starts in which the 22-year-old has netted seven times - almost a fifth of his entire tally since his move - set up another two, and provided a deft backheel in the build-up to Renan Lodi's goal which knocked out Manchester United in the Champions League.

"What we demand of him he is doing - he adds goals, talent, one-vs-one, vision, speed, aerial presence, defensive work. Everything is great for him."

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The young boy from Viseu, a small city around the size of Bath, has become a man, putting two tough seasons behind him to become Atletico's player of the month for both February and March on the back of a string of fine performances and returns. Against Manchester City on Tuesday, in the first leg of the quarter-finals, he will look to send his rising stock even higher.

That he started eight in a row to this point is already noteworthy in itself, and marks his longest run in Simeone's line-ups since his first season in Spain. His bit-part role since has not owed everything to form, with a succession of injuries hindering his consistency of both selection and performance.

That weight of expectation, externally at least, was matched by 13 La Liga goals and six assists across his first two seasons. If he was going to pay back his mammoth transfer fee, it was going to be in instalments.

Simeone doubled down on his faith in Felix last summer as Atletico rebuffed repeated efforts from Barcelona to take him to the Nou Camp. Eight months on it looks like that was a wise decision, but external onlookers were less convinced at the time. Felix's maturity, which saw him fire his way into the Benfica team so seamlessly as a teenager, would eventually pay its own dividends in La Liga.

Joao Tralhao knows Felix as well as anyone. He was a youth coach at Benfica when the forward was coming through the ranks, and never doubted his future prospects despite his up-and-down start in Madrid.

"He changed his reality, he changed his whole life aged 19," he tells Sky Sports. "Yes, playing for Benfica was demanding too but now he is in one of the big five leagues in the world.

"He went to a different club, different country, different language, different culture. You can imagine what that's like for any 19-year-old boy. I think in his first season he actually did very well, and the second season the same, considering his age.

"Of course, injuries have stopped him playing more regularly, but now you can see Joao. He's doing what everyone expected. In the last 30 or 40 years there are few examples of players who have achieved what he has done so far. Now, he's at the point where he can be one of the best players in the Atletico squad."

It only takes a look through the England line-up that beat Ivory Coast last week to show some players can cut it with the best while still in their teens, with Jude Bellingham a prime example.

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But equally look at Raheem Sterling, who broke into Liverpool's line-up as a 17-year-old. He has evolved as a player to reach double figures most years, but he did not break through the 10-goal barrier in a league season until he was 23.

Although very different players, that same self-determination which has taken Sterling to the level he is at today has underpinned Felix's evolution in La Liga.

A Simeone tactical reset, earlier this season, came at a perfect time too. With eight league games left, Atletico have already conceded more goals than in any full campaign under Simeone. Mid-season, Atletico have gone back to basics and returned to his well-drilled low block to find some defensive stability.

That style demands an out ball on the counter. And a counter-attack needs pace. The 35-year-old Luis Suarez still retains many qualities but they no longer include lightning speed; Felix too may not be Usain Bolt but his touch, technical control and passing have opened up the false nine role for him in that system to full effect.

More recently, that has evolved into playing as an out-and-out striker alongside Antoine Griezmann, with whom he has struck up a good partnership and a strong relationship. The pair were pictured wearing one another's shirts after the last-16 win over Manchester United, with Felix winning his elder's respect from the quality he is now showing on a regular basis.

"He always demands himself to be better every day," says Tralhao. "When I was his coach it was easy, because it made us completely co-ordinated. I would give him detailed plans with big targets, and he would always achieve them.

"He can play on the left side, he can play on the right side, he can play through the middle. I always see him as a false nine or an actual nine, but really the position doesn't matter. The most important thing is that the coach understands him, as Simeone does.

"He can play anywhere, because he always finds the spaces to do what the coach wants. He understands that positioning like few in the world, he's very clever. He just needs to be where he can demonstrate his quality."

Tralhao's praise is nothing on a well-publicised prediction he made in 2020, when he touted Felix as a future Ballon D'Or winner. Another 18 months on, he stands by it.

"My opinion hasn't changed at all," he says. "We cannot forget he was only born in 1999, so he is still very young.

"I look at potential indicators more than performance indicators, and he is playing in Spain, one of the best leagues in the world, and becoming better and better. There is still a lot of room for him to grow.

"I know him well, and I know his ambition. I know he has the capacity to still become one of the best players in the world."

Against Manchester City, he may go another step closer to proving it.