Martinez was with Bayern when Musiala was first breaking into the senior team.
The Spaniard told Marca: "In the Bundesliga you still have to fight for it. Anything can happen, there are always many ups and downs. Obviously, they are the big favourites. Let's hope that's the case and that Harry Kane can finally get the title that has eluded him. It's incredible.
"After 11 consecutive Bundesliga titles, he arrives for his first year at Bayern... and Leverkusen wins! We all want him to win his first title and break that curse.
"Jamal Musiala's stellar rise at Bayern is surprising? I already knew him from his first training session with us. You could already see that he was special. When he arrived in the first team he weighed 20 kilos (laughs). He was a 'naughty boy', as we say in Spain in a positive sense.
"It was even scary to tackle him because we thought we would hurt him since he weighed so little. But yes, as soon as he received the ball, you could see that he was special, that you couldn't take it away from him, that he was very fast, that he had the qualities of a champion. His evolution surprised everyone. We saw a great project, but I think his evolution has been even greater and that he has no limits. He will be among the top 10 in the world for many years to come."