LONDON, Jan 16 (Reuters) - Liverpool are seeking clearance from FIFA to sign Argentina midfielder Javier Mascherano from Premier League rivals West Ham United.'We have received correspondence from Liverpool and as in any other situation where a request is made a case has been opened,' said a spokesman for soccer's world governing body. FIFA rules state that while a player can register with three clubs during a season, classified as running from July 1 to June 30, he can only play for two teams in that period. Mascherano featured for Corinthians on his return from the World Cup in Germany before moving to West Ham in August. The 22-year-old joined along with international team mate Carlos Tevez but has featured in just seven games.