Nainggolan insists the Scotsman lacks the technical qualities to be mentioned in the same conversation as the great midfielders of his generation.
The former AS Roma and Inter Milan midfielder was speaking on Sky Sport's Calcio Unplugged, where he covered the season's title race, his own playing career and a series of pointed assessments of the current crop of Serie A players.
On Inter's title credentials, Nainggolan was unequivocal.
"If you asked me at the start of the year who could win the Scudetto, I would always have said Inter. Their squad is superior and they are the ones who play best. They brought in some quality young players like Esposito, and behind that there weren't many changes. They did well. Napoli and Milan were close but they don't have the continuity Inter have. That's not strange to me."
On McTominay, who won last season's Serie A player of the year award and has contributed 23 goals and assists across his first 18 months at Napoli, Nainggolan was blunt.
"I don't like him. He scores a lot of goals — he'll always get 12, 13, 14 — but if he has to build play he doesn't have the technique to play between the lines. He is a normal player."
He was equally direct when asked to rank himself against the midfield elite.
"In my prime I was better than him and Calhanoglu, but I put Barella above me. De Bruyne and I are different, but he really appeals to me — he sees things others don't see, I put him above me. I prefer myself to Rabiot. Koné and I can't even be compared. But if you mention Modric — he has always been among the strongest in the world. The greatest of all time for me was Dembélé, then I put Xavi and Iniesta."
Nainggolan spent 11 years playing in Italy without winning a Serie A title, finishing runner-up with Roma in the 2017/18 season and not qualifying for a medal during Inter's 2020/21 championship. The authority with which he judges those who have succeeded where he fell short has not diminished with age.
Inter lead the Serie A table with five games remaining. A win in their next fixture would put the title beyond Napoli's reach.