The 24-year-old defender, who was on trial at the Premier League club last week, is currently in South Africa for Zambia's 2013 Africa Cup of Nations campaign.
"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," Hammond told the club's official website.
"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."
Hammond added that Reading will continue their negotiations over a deal with TP Mazembe.
"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," he said.
Sunzu joined TP Mazembe in 2009.