The veteran British driver, who was replaced by his fellow Briton, Mark Blundell, for the races in Brazil and Argentina, said: "The kindest thing to say is that there was a definite design mistake made."
Mansell made his comments after a test session at Silverstone and is expected to make his long-awaited racing return after two years in IndyCar racing - during which he also became champion in his rookie season - in next week's San Marino Grand Prix at Imola.
"It was a big disappointment when I was forced to miss the first two races and it was a brave decision by McLaren and by myself, but what I've found out in the last couple of days is that it would have been impossible to drive," Mansell said.
"We made the right choice. It would probably have been a disaster if we had tried to take part in the first couple of races."Reuse content