Liverpool are trying to sign Colombia winger Luis Diaz from Porto in the current transfer window.
The deal, if completed, is expected to be worth €45m (£37m) plus a maximum of €15m in potential bonuses.
Liverpool were planning to wait until the summer but that changed as it became clear that if they did not act now the player would move elsewhere.
The player had been linked with a move to Tottenham, who reportedly had a bid of around £38m rejected.
Diaz was Liverpool boss Jurgen Klopp's first choice for the summer when the asking price would have been €60 million (£49.