The news of Foyth's arrival comes not long after Tottenham confirmed former fringe defender Kevin Wimmer had agreed a move to Premier League rivals Stoke City after making just 31 appearances in two years at the club.
The teenager is unlikely to play regularly for Spurs' senior side this season but Pochettino will monitor his progress closely for the club's youth teams.
Foyth also featured for the Argentina Under-20 national team in this summer's World Cup tournament in South Korea where he played the full 90 minutes in every single match.
At one point it appeared Mauricio Pochettino could lose out on his compatriot altogether, as Paris Saint-Germain also registered their interest.More news: TDP pips YSRCP in Nandyal bypoll
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Tottenham haven't disclosed the precise details of the fee but the BBC claim they have paid Estudiantes around £8m, which could turn out to be a shrewd piece of business by the Londoners.
"My agent knows what leagues attract me and Russian Federation is not one of them in this moment", he told Radio Continental.
Juan - 'It's a club that believes in young players and I'm very pleased to be here.' Embed from Getty Images What else do we know?
Foyth said: "I really like this club".
The Argentine is Tottenham's third signing after securing the signatures of center-back Davinson Sanchez from Ajax and goalkeeper Paulo Gazzaniga from Southampton.