  The attenuation of very high energy (VHE) photons by the extragalactic
background light (EBL) prevents the observation of high redshift flat spectrum
radio quasars (FSRQs). However, the correlation of VHE spectral index with
source redshift suggests that EBL intensity may be less than what is predicted.
This deviation can draw new constraints on opacity of the universe to VHE
gamma-rays. Therefore, more FSRQs may fall above the sensitivity of the
forthcoming VHE telescopes than the ones predicted by the existing EBL models.
In order to account for the lower EBL intensity predicted by the index-redshift
correlation, we introduce a redshift dependent correction factor to the opacity
estimated from commonly used cosmological EBL model. Considering this modified
opacity, we identify the plausible VHE FSRQ candidates by linearly
extrapolating the \emph{Fermi} gamma-ray spectrum at 10 GeV to VHE regime. Our
study suggests among 744 FSRQs reported in \emph{Fermi} fourth catalog-Data
release 2 (4FGL-DR2), 32 FSRQs will be detectable by Cherenkov Telescope Array
Observatory (CTAO). Since the FSRQS are proven to be highly variable, we assume
a scenario where the average \emph{Fermi} gamma-ray flux increases by a factor
of 10 and this predicts additional 90 FSRQs that can be detected by CTAO.
