We present VTL/ISAAC infrared spectroscopy of a sample of short orbital period cataclysmic variables which are candidates for harboring substellar companions .
We have detected the K i and Na i absorption lines of the companion star in VY Aqr .
The overall spectral distribution in this system is best fit with a M9.5 type dwarf spectra , implying a distance of 100 \pm 10 pc .
VY Aqr seems to fall far from the theoretical distribution of secondary star temperatures around the orbital period minimum .
Fitting of the IR spectral energy distribution ( SED ) was performed by comparing the observed spectrum with late-type templates .
The application of such a spectral fitting procedure suggests that the continuum shape in the 1.1-2.5 \mu m spectral region in short orbital period cataclysmic variables may be an useful indicator of the companion spectral type .
The SED fitting for RZ Leo and CU Vel suggests M5 type dwarf companions , and distances of 340 \pm 110 and 150 \pm 50 pc , respectively .
These systems may be placed in the upper evolution branch for short period cataclysmic variables .