Fifa regulations may prevent West Ham midfielder Javier Mascherano from joining another club this season.
Under the world governing body's rules, a player cannot play competitively for more than two different clubs between 1 July and 30 June the following year.
Already, Mascherano has played for Brazil's Corinthians and West Ham.
And with Mascherano allowed only to register, but not play, for a third club, a reported loan move to Liverpool would be very unlikely to happen.
A Fifa spokesman confirmed: "Our understanding, as of today, is the rule is binding.
"If I am not playing in the West Ham team I will have to leave to continue my career"
"There is no provision that allows for any kind of waiving of this rule."
Mascherano, 22, arrived at Upton Park along with international team-mate Carlos Tevez on 31 August.
But he has played just six minutes since the defeat at Tottenham on 22 October and is desperate to leave the club.
On Thursday, Mascherano said: "I cannot stay at West Ham any more like this, without playing. At my age, my game will stagnate if I don't play.
"I came to England to do well but I have not had the opportunities necessary to show what I can do.
606: DEBATE
"If I am not playing in the West Ham team I will have to leave to continue my career with another team."
Italian side Juventus reportedly pulled out of a move to sign Mascherano citing the complications with the player's contract.
Mascherano has played in seven games since joining West Ham in August, five in the Premiership and the two Uefa Cup ties against Palermo.
Struggling Hammers boss Alan Curbishley has been linked with West Brom's Nigel Quashie as a replacement for Mascherano.
The 28-year-old midfielder joined the Baggies from Southampton in January 2006 and has vast experience of battling against relegation.