Zhang won his second gold medal of the London Games in the men's team final earlier today, having previously won gold in the singles tournament.
The 24-year-old has also won in the World Cup and World Championships, and Liu believes that his monopoly of the sport is not over yet.
"He played very well," said Liu. "He challenged himself and I think he deserves to win the two gold medals.
"He put in a great effort during training, but I still hope that he can do better in the future and take over men's table tennis.
"I want him to lead the whole men's team and get better results."
China's team gold ensured that they collected every available table tennis gold medal at this Olympic Games.