Borussia Dortmund completed the signing of Argentina Under-20 defender Leonardo Balerdi from Boca Juniors.
The centre-back has only made five league appearances for the beaten Copa Libertadores finalist, but is regarded as a top prospect, with Dortmund paying a fee reportedly in the region of €15 million.
"The acquisition of Leonardo Balerdi was originally planned for the summer but has been brought forward," Dortmund sporting director Michael Zorc said. "Leonardo is an intelligent centre-back and strong defensively. He also has a good build-up and passing game.
"We are very glad that he has chosen us and we're convinced that he will help us with his talent in the future."
The 19 year-old has signed a "long-term contract" with Dortmund and will hope to flourish at a club renowned for developing young players.