Cristian Romero has completed his move from Atalanta to Tottenham for a fee in the region of £42m.
He completes his switch to north London having helped Atalanta to a third consecutive third-placed finish in Serie A last season.
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The defender, who has won five caps for Argentina, adds to new boss Nuno Espirito Santo's defensive options following the departure of Toby Alderweireld last month.
Tottenham are expected to look to sign one more defender ahead of the new season and remain in talks with Bologna over Takehiro Tomiyasu. However, Colombia international Davinson Sanchez has been made available for transfer.
Romero's arrival also comes amid continuing uncertainty over the future of striker Harry Kane.
The England captain failed to report for training earlier this week but took steps on Friday to clarify his absence and confirmed he would return on Saturday.
Tottenham kick-off their Premier League campaign at home to Manchester City on August 15, live on Sky Sports.
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'There's plenty to like about Romero'
South American football expert Tim Vickery:
"Centre-back has been a real problem position for Argentina for years and just since the start of June when he first played, Cristian Romero has been greeted as the saviour. Even with just five caps, he's now the first defender on the team sheet for Argentina.
"He had a few injuries during the Copa America and only played three games, but Argentina didn't concede in those three games and had a splendid season at Atlanta, who are an attacking club. Their defence was often exposed but he came through that very well.
"He's combative - sometimes a little too combative - he's 23 so there's a lot of football ahead of him. Tottenham may be paying a little over the odds for him, but there's plenty to like about him. He's a real fighter."