Highly accurate soft-XMCD data recorded on a Nd2Fe14B single crystal, through the spin reorientation transition show that the average Fe orbital moment is proportional to the macroscopic Fe anisotropy constant, and diverges 15 K below the reorientation transition temperature. This divergence is indicative of a critical behavior and it is related to a tetragonal distortion. These results give experimental evidence of the mutual dependence between orbital moment, macroscopic magnetic anisotropy and tetragonal distortion.