The 18-year-old Dutchman endured a horror outing last weekend just two weeks after winning in Spain.
"It was a terrible weekend for him," he told Motorsport-Magazin.com.
"He's fast but he made too many mistakes."
Verstappen was drafted into Red Bull's race lineup after the Russian Grand Prix, where his predecessor Daniil Kvyat had caused a first-lap crash which according to Dr Helmut Marko was the result of him not coping with pressure.
Then in Monaco, Verstappen made at least three driving mistakes, including hitting the barriers in qualifying which left him at the back of the grid and then a race-ending crash the following day.
"Another driver would now be sent home," Villeneuve claims, "but because it's Max Verstappen, people start to make excuses because he is protected."
Asked if Verstappen's crashes might be justified on the basis that he was trying to make up for not having the same engine specification as his teammate Daniel Ricciardo, Villeneuve said: "Of course not.
"He made the same mistake twice, which is unacceptable, but three errors in a weekend is just too much.
"But he is loved by Red Bull, loved by the fans - he is loved by everyone."
Nonetheless, Villeneuve thinks that Verstappen does have the potential to be world champion one day.
"If he learns from his mistakes then yes," said the French Canadian. "But if he has to go over the limit to be fast, it means he is not fast enough."
The season continues with the Canadian Grand Prix next weekend.