United States international Yunus Musah joined Atalanta on loan from AC Milan shortly before the transfer window shut on Monday.
Neither Serie A team gave financial details of the deal, but Italian media reports said Atalanta paid €4 million ($4.7m) for the loan to the end of the season, when it will then have the right to sign the midfielder permanently for €24 million ($28m).
Musah, who was born in New York but grew up in Italy and England, has featured in the majority of Milan's matches since joining from Valencia two years ago.
The 22-year-old has also made nearly 50 appearances for the U.S. since his debut in 2020. He was also eligible to play for England, Italy and Ghana.
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Atalanta finished third last season but is struggling since coach Gian Piero Gasperini left for Roma after nine years in charge. It has drawn both of its league matches against promoted Pisa and at Parma.
Atalanta hosts Lecce in Serie A on Sept. 14, after the international break, before opening its Champions League campaign against holder Paris Saint-Germain.