Atletico Madrid have sold Rafael Santos Borre and Matias Kranevitter with Luciano Vietto also close to leaving the club.
Colombia under-21 forward Santos Borre moved to Atletico in summer 2015 but spent the 2015-16 season on loan at former club Deportivo Cali and the following one on loan at Villarreal.
The 21-year-old never featured competitively for Diego Simeone's side, and reports said River Plate were paying €3 million for him with Atletico holding 50 percent of his rights ahead of any future transfer.
An Atletico statement said: "Atletico Madrid and River Plate have reached an agreement for the transfer of Rafael Santos Borre.
"From Atletico Madrid, we wish him the best of luck in this new phase."
Kranevitter, who joined for around €8m in January 2016 and spent last season on loan at Sevilla, will join Zenit St Petersburg after Atletico and Zenit confirmed a deal had been reached over the Argentina international's transfer.
The 24-year-old attended Zenit's 5-1 home win over Spartak Moscow last weekend and will move in a deal reported to be worth €8m.
Vietto, who joined from Villarreal for €20m in summer 2015, also spent last season at Sevilla.
Earlier this summer, sources told ESPN FC that Southampton were interested in him but no move has yet materialised.
However, goalkeeper Jan Oblak is set to stay despite reports that Paris Saint-Germain could pay his €100m release clause.
Marca reported that Oblak should soon sign a new contract with Atletico, even though his current deal was agreed less than 18 months ago.