In the 2018-19 campaign, Felix scored 20 goals and provided eight assists for Benfica to become the most coveted teenager in football, winning the Golden Boy award given to the game's most exciting young player. It tempted Atletico Madrid to splash out £113m - the fourth-highest transfer fee in history - on a player who was still only 19.

He was expected to explode into global superstardom, but it didn't happen. After scoring just four goals in his first 22 starts for Atletico, the Portuguese lost his place in the team and has struggled to get it back ever since.

True, Felix was part of Atletico's title-winning team last season. But he didn't play a particularly significant part, especially in the decisive stages of the campaign as he failed to start or score in any of the final eight La Liga games.

The widespread conclusion was that Atletico boss Diego Simeone simply did not trust Felix, whose technically gifted, but physically-deficient profile, has rarely made him look like a natural fit for the exuberant Argentine coach.

Until recently, Atletico Madrid boss Diego Simeone had only given Joao Felix fleeting starts in the team.

One obvious criticism of Felix is a less-than-wholehearted attitude off the ball. So far this season, for example, he has averaged 9.1 pressures of the opposition per game, only slightly more than 35-year-old Luis Suarez (8.3) and far fewer than fellow forwards Antoine Griezmann (21.5), Matheus Cunha (20.4) and Angel Correa (19.5).

For a coach such as Simeone, who values work-rate and tenacity above all other attributes, that will always be a problem - especially when combined with Felix's undeniable creative ability on the ball only making sporadic appearances.

As recently as six weeks ago, it seemed inevitable this would become another season to pass Felix by. He had only started six league games out of 24 and his nimble talents appeared to be the last thing on Simeone's mind as he attempted to guide his team out of a slump that had seen them lose seven of their last 12 games.

A trip to Osasuna on 19 February, however, proved to be an unexpected turning point both for Felix and the team.

He was selected to start, scored after just three minutes and later provided an assist for Suarez's second in a 3-0 win. Four days later, he started again in the first leg of the Champions League last-16 meeting with Manchester United - and again scored an early goal, a leaping near-post header to give David de Gea no chance.

Joao Felix scored against Manchester United in the Champions League in February.

Since then, Felix has stayed in the team - making eight consecutive starts for the first time in more than two years - and continued to deliver the goods: two goals in a 3-1 win at Real Betis, an early strike to help defeat Cadiz, a prominent role in the build-up to Renan Lodi's tie-winner at Old Trafford; an assist for Koke's winner at Rayo Vallecano and another brace in Saturday's 4-1 victory over Alaves.

Madrid-based football journalist Euan McTear, who wrote a book on Atletico's 2014 title triumph, believes there's still a lot more to come.

"I don't think it's a coincidence that his recent run of good form has coincided with a run of consecutive starts," McTear told BBC Sport. "He needs to start each day at the office well and that's easier to do from the starting line-up.

"We have to remember he's still only 22, so he isn't supposed to be the team's leader yet. But, there's no doubt that, in time, he will be the star man for the club - that's why he signed a contract until 2026. Even if some say he isn't at the right club, he can still become one of the best in the world."

As noted by McTear, there is an ongoing debate Felix may only be able to truly flourish away from Atletico - and the defensive discipline demanded by Simeone.

Despite his struggles to justify his price tag for Atletico, Felix's ball-playing talents have always been obvious and he still has plenty of admirers. Only last week Barcelona president Joan Laporta admitted he attempted to bring Felix to the Nou Camp in a swap deal with Griezmann last summer, and it's easy to see the logic in such a move.

Conversely, other observers counter Felix's mercurial talents are exactly what Simeone needs to take Atletico to the next level, moving away from the old reliance on ground-out 1-0 slugfests and developing a more attractive, expansive style of play.

Recent results - six consecutive league wins plus the Champions League triumph against Manchester United with Felix in the starting line-up - support that argument.

And although his longer-term future remains in some doubt, right now Felix is clearly in the best form of his Atletico career - and arguably their most important player.

A pair of strong performances to defeat the mighty Manchester City could propel him to the next level.