West Ham midfielder Javier Mascherano has been given permission by Fifa to join Liverpool from West Ham.
Under Fifa’s rules, a footballer cannot play for more than two different clubs between 1 July and 30 June the following year, but Fifa have made a special dispensation in Mascherano’s case.
Mascherano, 22, has already played Corinthians and West Ham in the last 12 months.
But Fifa said: “The Fifa single judge ruled that Javier Mascherano is eligible to play in official matches with Liverpool with immediate effect.”
“FIFA looked at this from a global perspective and the overlapping aspect of the seasons was taken into account,” added a spokesman.
Mascherano arrived at Upton Park with international team-mate Carlos Tevez on 31 August, but he has played only six minutes since the defeat at Tottenham on 22 October and has been desperate to leave the club.
Liverpool coach Rafa Benitez told the club’s website: “He will give us options and is a very good character.”