The Serie A giants signed the French midfielder on loan from Tottenham towards the end of the summer transfer window.
Only one of his three appearances so far have come in the starting eleven and even then he was taken off at half-time against Lecce last weekend.
Giuntoli conceded that Ndombele is lacking match fitness at the moment and despite having wonderful qualities, he has missed too much football already.
He insisted that Napoli coach Luciano Spalletti will gradually ease him in and get into the physical condition needed to play on a regular basis for the club in the ongoing campaign.
“He is a bit out of competition”, Giuntoli said on Italian radio station Radio Kiss Kiss.
“He has great qualities but you also notice that he is struggling because he misses games.
“The coach must be good to get him into condition slowly.
“We had already dealt with him a few years ago, the good relationship with Tottenham helped us.”
Fitness has been a major issue for Ndombele since he joined Spurs and successive Tottenham managers seemed to be left unimpressed by his conditioning.
It remains to be seen whether he can turn the tide of his career in Italy at Napoli this season.
