Atletico Madrid and Argentina defender Nahuel Molina. File photo: AFP.
Atletico said the 24-year-old Molina has agreed to sign a five-year contract. The right back will help fill a void left by the departure of England's Kieran Trippier midway through last season.
Molina scored 10 goals in 68 appearances over two seasons for Udinese. Before his move to Italy, he played for clubs in Argentina after coming up through Boca Juniors' youth teams.
He helped Argentina win the Copa America last year, playing in five games before missing the final against Brazil.
Neither club disclosed the transfer cost.
Atletico has also signed midfielder Axel Witsel and winger Samuel Lino this summer as it tries to bounce back from finishing a distant third in Spain last season.
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