The Mirror says the Argentina midfielder is currently on a long-term loan deal at Anfield that runs until the summer.
Because he is owned by his agents MSI, not a club, he is effectively classed as a free agent and can be signed outside of any transfer window. A fee of £17.1million has been verbally agreed.
Mascherano said: "It's not finished yet but I am happy that I will be staying here. We need to wait but we are very close."