I question the translation "natural man." Exegetically, ψυχικὸς doesn't mean "by nature." It means literally "of the soul" or "soulish" and pertains to those functions which constitute animal life: the senses, basic instincts, motion. The idea seems to be someone who, lacking the heavenly perspective awakened by the Spirit, concentrates on the transitory things of this world.
Theologically, a sinner is not a "natural" man. Sin is a corruption of the good nature that God created. Human faculties are good in their substance, evil only in their orientation and effects.
The NIV says "man without the Spirit," loose but conceptually accurate. The NET gives "the unbeliever," too loose, in my opinion. The Douay-Rheims reads "sensual man," the best out of all.