Best Peruvian players who never played a World Cup IMO: Teodoro "Lolo" Fernández Juan Joya Valeriano López Juan Seminario Alberto "Toto" Terry Guillermo Delgado and Julio Meléndez were probably the best Peruvian central defenders behind Héctor Chumpitaz. None of them played a World Cup. Neither Canhoteiro. Both were probably the best Brazilian left-wingers ever but when they could have played were displaced by Mário Zagallo, much less talented in individual terms.
apparently juan RAMON veron was the best player of estudiantes lp, when they won 3 libertadores in a row. anibal tarabini was selected instead of him for the 1970 wc qualifiers and argentina failed to qualify. i thought this to be a worthwile mention.
Gary Pallister Roy Makaay Alexsander Hleb Samir Nasri (maybe still an outside chance as he's 29 but he did retire from the French national team a couple years ago and there are no signs he will be back in the fold)
Djalminha. He missed the 2002 World Cup because of an argument in training and ended up head-butting his then manager at La Coruna, Javier Irureta. This made Scolari give up on him and call up a young Kaka instead.