Nainggolan has revealed AC Milan will welcome Cristiano Ronaldo to the club, should Real Madrid discard him.
Ronaldo has been under heavy criticism this season, despite having 32 goals in 30 matches.
And Nainggolan believes the height Ronaldo set for himself makes him easily criticised.
“The only thing that I see is that he scores goals every week. If they don’t want him, I’d love him to come to Roma,” he told Marca when asked if had seen a decline in the Portugal captain’s performances.
“It’s normal that these great players are questioned. They are global stars and they have themselves to blame for being so good.
“Cristiano and [Lionel] Messi generate such expectation around the world that, once they’re down just a little, people get worried unfairly.
“They’re one of the best teams in the world. You can never doubt that.”
Ronaldo and Madrid travel to the Stadio Olimpico to take on Roma on Wednesday in the first leg of their Champions League last-16 tie, and Nainggolan concedes Luciano Spalletti’s side need a “miracle” if they are to progress to the quarter-finals.
“Facing Real Madrid will help us to know where we are in these moments, where we find ourselves in respect to these teams,” he added.
“The Olimpico will help us to be better. We’ll try to cause some distress for Real Madrid.
“We play at home and we have to get a good result for the return game. Okay, we’ll try to pull off a miracle, perhaps I should say.”