Nmecha fired Germany into the lead with a whipped finish into the far corner in just the sixth minute of their 7-1 demolition of Curacao in Houston, and the performance underscored why the 25-year-old has become one of the most coveted midfielders in the Bundesliga.
According to Bild and Sky Germany, Real Madrid manager Jose Mourinho has made personal enquiries about Nmecha's availability, with the Portuguese keen to add energy and creativity to a Madrid midfield that has already been reshaped this summer.
Mourinho has already signed Marc Cucurella from Chelsea and completed deals for Ibrahima Konate, Denzel Dumfries and Bernardo Silva, but the German midfielder is understood to fit a specific profile Mourinho is looking for in the centre of the park.
Manchester United and Manchester City have also been keeping tabs on Nmecha for several months, with both clubs aware of his ability to operate in multiple central midfield roles.
Borussia Dortmund are in a strong position, however, having moved decisively in March to extend Nmecha's contract until 2030, effectively shutting the door on any cut-price approach.
The deal includes a release clause valued at €80 million, but that option cannot be activated until the summer of 2027. A further clause worth €70 million then comes into effect in 2028.
That means any club wishing to sign Nmecha this summer would need to agree a fee directly with Dortmund that significantly exceeds those trigger points — a prospect the Westfalenstadion outfit have shown no appetite for.
Dortmund sporting director Ole Book has stated publicly that Nmecha will not leave the club this summer, a position the club's hierarchy have maintained consistently despite the growing noise around the player.
Nmecha arrived at Dortmund from Wolfsburg for €30 million in 2023 as a replacement for Jude Bellingham, and has made 112 competitive appearances for the club since then, contributing 13 goals and eight assists.
His importance to Niko Kovac's side is considerable.
"Felix is developing in a good direction," Kovac said.
"He is our metronome in midfield and directs and leads our game. We need him."
For Manchester United in particular, the interest carries a personal dimension. Nmecha came through Manchester City's academy as a teenager before departing and building his career on the continent, making his eventual return to English football a compelling narrative whatever club it eventually happens for.
His World Cup performances will only add to the speculation. Germany's next Group E fixture is against Ecuador, and Nmecha is expected to be central to Julian Nagelsmann's plans throughout the tournament.