Martinez took Manchester United midfielder Cleverley to Wigan on loan in 2010-11 and holds the 24-year-old in the highest regard.
More than 15,000 fans have signed an online petition to keep Cleverley out of England’s World Cup squad and his name was booed when it was read out before the friendly against Denmark on Wednesday night.
He said: "I don’t understand it. Tom is part of this new generation of outstanding English talent.
"There are only a few players who look as if they could have been brought up in Holland or Spain or France because of their understanding of the game, their tactical awareness and their technical quality. Tom has got that.
"Then as a boy, he has got the perfect temperament. He is a level-headed boy. I just don’t understand this campaign. Tom was maybe given a bigger role than he should have been given but all of a sudden he is being judged like this? He’s young. He hasn’t played 200 Premier League games. It’s not his fault."
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