  We calculate the charge compressibility and uniform spin susceptibility for
the two-dimensional (2D) Hubbard model slightly away from half-filling within a
two-loop renormalization group scheme. We find numerically that both those
quantities flow to zero as we increase the initial interaction strength from
weak to intermediate couplings. This result implies gap openings in both charge
and spin excitation spectra for the latter interaction regime. When this
occurs, the ground state of the lightly doped 2D Hubbard model may be
interpreted as an insulating spin liquid as opposed to a Mott insulating state.
