  We present a new method to subtract sky light from faint object observations
with fiber-fed spectrographs. The algorithm has been developed in the framework
of the phase A of OPTIMOS-EVE, an optical-to-IR multi-object spectrograph for
the future european extremely large telescope (E-ELT). The new technique
overcomes the apparent limitation of fiber-fed instrument to recover with high
accuracy the sky contribution. The algorithm is based on the reconstruction of
the spatial fluctuations of the sky background (both continuum and emission)
and allows us to subtract the sky background contribution in an FoV of
$7\times7 arcmin^2$ with an accuracy of 1% in the mono-fibers mode, and
0.3-0.4% for integral-field-unit observations.
