The Giallorossi coach believes the Belgian midfielder is destined to become a major hit at the Stadio Olimpico
The 25-year-old joined Roma from Cagliari in the January transfer window and Garcia has little doubt that the midfielder will become a key figure at his new club.
"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," Garcia 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."
Nainggolan has so far made five appearances in all competitions for Roma.