The 25-year-old joined from Cagliari last month, and Garcia insists that he is exactly the type of player he was looking for.
"Nainggolan is a top player. We did not only sign him to help us qualify for the Champions League, but for the long-term future as well," he told RTBF.
"We do not see him as the ideal 12th man, but as a potential starter for us. He can still improve going forward and become a box-to-box midfielder.
"He can become even more decisive for us, but he's already very important. He knows how to play one-touch football, is physically very strong and has vision. He's exactly the type of player we were looking for."
Garcia has won four caps for the Belgium national side since making his debut in 2009.