River Plate sign midfielder Manuel Lanzini after West Ham departure
"Lanzini is a River player. We closed an agreement a few hours ago. He is today a free player and will be coming for a period of one year," club president Jorge Brito told local television.
"Manuel will be a unique player in Argentine football because of the level of play he comes from; he is very important for us."
Lanzini returns to River, where he began his career in 2010 before spells at Fluminense in Brazil, Al-Jazira in the United Arab Emirates and West Ham, where he made more than 200 appearances between 2015 and 2023.
River clinched the Argentine league title last month and on Tuesday got a 2-1 home win over Internacional of Brazil in the first leg of their Copa Libertadores round-of-16 tie.