Reading are keen to sign the Zambia defender after he impressed on trial at the Madejski Stadium earlier this month.
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 stint in Berkshire last week.
However, an obstacle to the deal is a problem that has emerged with his contract situation at TP Mazembe.
Sunzu believes his contract TP Mazembe expired in December 2012, while the Congolese outfit claim the 23-year-old is under contract until 2015.
A source close to the player said that the player is very upset and cannot understand what the hold-up is, feeling he is now ready for the next step in his career by moving to the Premier League after three seasons at Mazembe.