Udinese have gone to the Court of Arbitration for Sport over fees owed to them by Portsmouth for Sulley Muntari.
The midfielder joined Pompey from Udinese in the summer of 2007 and spent a successful 12 months at Fratton Park before moving back to Italy with Inter Milan.
However, Udinese claim they still have not received 4million euros (£3.5m) from the South Coast club and have reported the matter to CAS.
The precarious financial situation at Fratton Park left Portsmouth still owing money to several clubs for previous transfers at the start of January.
Pompey were therefore banned from registering new players and the embargo would not be lifted until they had paid their creditors.
Debts have since been settled with UK clubs as well as French duo Lens and Rennes.
It is believed the Premier League had withheld some of Portsmouth's television money to Udinese last week because they were awaiting evidence of an agreement between the two clubs.
But Udinese's appeal to CAS suggests any deal is not to their satisfaction.
Portsmouth must now focus on resolving the issue with Udinese and reports indicate the Premier League will then allow the club to start signing players again.
Portsmouth say an appeal date has yet to be set.