Atletico are locked in talks with River over a fee for the youngster.
"We all know that it's very difficult to retain for a long time players that have the quality that Erik has," River coach Juan Jose Lopez stated.
"We all know that a team with a lot of money can take him away at any moment, and nobody, neither the president or me want to stop a player's career.
"If his transfer is something good for River and for the player then I hope he gets transferred to Europe and I wish him all the success. But before that all we want to do is win a title."