This trophy is awarded for winning any of the top leagues in Master League, like it says on the tin. The difficulty level doesn't matter, and you get the trophy as soon as you win the title - not at the end of the season. I won it playing in the Belgian Jupiler Pro League, which tells me the definition of 'top league' is not one of the Big Five (England, Germany, Spain, Italy, France) but just whatever the top league of that country is (so not Ligue 2 for instance).