Capellas spent 11 years inside the Barca coaching system and is now No2 to new BVB boss Peter Bosz.
He told Sport: "Dembele is pure talent, extreme skill, direct, uses both feet and has an extra point of speed in short space that makes him different, he seems not to arrive and there he is.
"He is definitely a different player, a talent out of the ordinary, special.
"Neymar? I do not like to compare and that's why I'm not going to do it. Let him be himself, not try to resemble anyone."