Sunzu, who is currently away with Zambia at the Africa Cup of Nations, was hoping to finalise the move to Reading this week after agreeing personal terms and passing a medical during his trial stint in Berkshire last week.
However, the move has been delayed after a problem with his contract at TP Mazembe emerged.
Sunzu believes his deal at TP Mazembe expired in December 2012, while the Congolese outfit claim the 23-year-old is under contract until 2015.
The 23-year-old's representative, Paul Carew, has now appealed to TP Mazembe to return Sunzu's contract to his client so that his move to Reading can be concluded.
"Stoppila is upset that things are dragging on. He signed a three year contract with TP Mazembe and now that it is up he wants to move on," Carew told skysports.com.
"Mazembe are refusing to give Sunzu his playing contract which he has requested in writing and which will prove that he is a free agent.
"We have asked for help from FIFA and the English FA to solve this problem but whatever happens Sunzu will not be returning to Mazembe."