Sunzu, 24, was on trial at Reading last week, but has had to fly to South Africa to help his country's defence of their African Nations Cup title.
Reading were impressed with how the centre-back performed during his spell at the club, with whom he also trained six years ago, and will continue their dialogue with the player's DR Congo-based club over the forthcoming weeks.
Director of football Nick Hammond told Reading's website: "We had a very good week with him here, we had been trying to bring him across since the summer and this was the first opportunity we had. He was here as a young boy a few years ago so it was great to see him again.
"We're very grateful to his club TP Mazembe for allowing him to train with us, they have been a pleasure to deal with throughout the entire process. Of course the same also goes for the Zambian FA who were also very gracious in allowing him to train with us so close to the start of the Cup of Nations.
"Now of course his focus will be fully on the tournament and doing well for his country, so we will continue to monitor his performances and will continue our dialogue with TP Mazembe."
- Sports & Recreation