Martinez has lived and worked in the UK for 19 years and insists he has never encountered anyone quite like the 20-year-old midfielder.
He told the Daily Mail: "Nothing fazes Ross. That temperament, I'm not sure we've seen that too often over the years.
"For some reason, the English talent is often the naughty boy. It's a short fuse, or he gets into some kind of trouble. Drinking, smoking.
"Ross is the opposite. I think partly because he had a big injury at 17 (he broke his leg in three places). All of a sudden something took it all away from him. He realised what he could lose. But home is good too. He's well-grounded. His mum is a great influence. He's one in a million."
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