Neymar has been slated, especially in Britain, for diving, rolling and exaggerating fouls.
Mexican coach Juan Carlos Osorio made a reference to "too much acting" and former internationals Alan Shearer, Pat Nevin, Peter Schmeichel and Eric Cantona were among those who criticised Neymar's theatrics during the first four games of the tournament.
But Ronaldo said Neymar – who is one of the most fouled players in the entire tournament - needed more protecting.
"There are many ways to see football and interpret it," Ronaldo told reporters. "I am against all these opinions (on Neymar acting). He is an intelligent player in his movements and on how to defend himself from being tackled. I don't think referees have been protecting him enough.
"When people repeatedly hit me I would feel a sense of unfairness. Criticism is nonsense. TV shows and newspapers just want to fill the space."
Ronaldo's comments came as fans and pundits, many of them Brazilians, hit out at what they saw as play-acting by English players in their shootout win over Colombia.
Brazilians who watched Jordan Henderson go down clutching his forehead after being hit under the chin and Harry Maguire diving in the box want the same rigid criteria to be used as when judging Neymar.
"What they are saying about the theatrical and pathetic performance of English players yesterday?" Elena Landau, a Brazilian lawyer who used to advise Rio club Botafogo, asked on Twitter. "In Brazil, as you know, we have a saying...'Envy is a bitch'."
Landau's comment came after Colombian coach Jose Pekerman accused the England players of going down too easily in search of fouls.
Manchester United manager Jose Mourinho also singled out Maguire, "normally a very honest guy...for diving in the box.
"People are focussing on Neymar, but if it was only Neymar, I'd be happy, but it's not only Neymar," Mourinho said on Russia Today after England's win.
"Every team has lots of diving, lots of pretending, lots of putting pressure on the referee...the game loses quality...and for me that was the negative point."
(Reporting by Andrew Downie, editing by Neil Robinson)
