Sosa, who has five Argentina caps, has been loaned to Estudiantes by Bayern Munich until June 30 but the club from La Plata have so far been unsuccessful in trying to obtain his FIFA clearance before the transfer window.
The 24-year-old, who joined Bayern from Estudiantes for $8.9 million in 2007, has yet to play for the Argentine club since returning to them at the end of October.
Estudiantes were allowed to take centre back Rolando Schiavi on loan from Newell's Old Boys in mid-year due a glut of injuries to defenders. He played four times for Estudiantes, helping them win their two-legged Libertadores Cup semi-final and final.
The December 9-19 club tournament brings together the champions of FIFA's six confederations with Estudiantes and European Cup holders Barcelona given a bye into the semi-finals.
