That is the claim of new McLaren team boss Eric Boullier, who at his former team Lotus helped to get the latter two drivers up to speed in formula one.
In Danish rookie Magnussen's case, the 21-year-old got his F1 career off to a stellar start in Melbourne with a debut podium, but his and McLaren's form has since dipped.
Boullier said Magnussen's progress "reminds" him of Russian Petrov and Frenchman Grosjean at Lotus.
"They went through the same processes and it's part of the learning curve, unfortunately," he said. "They need experience, they need to be able to understand the car.
"The F1 car – setup wise – is much more complicated than the junior categories, so it's just part of the learning progress. And he's not helped by the fact that he has a car that is not so easy to drive today," Boullier added.
Magnussen agreed that the four races so far in 2014, including the more difficult run since Melbourne, have been good for "learning".
"At this point for me it's all about learning," he said. "I need good results but I need to learn along the way as well."