Only 16, Thill is already a first teamer with Metz and an international with Luxemburg.
The midfielder's agent stated last week that Real Madrid had been monitoring his development and been in contact.
And City are also keen, having posted scouts to watch Thill in action for Luxembourg during international week.
Metz youth chief Denis Schaeffer said yesterday: "He has the potential to one day be in a club of the top five of Europe."
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