  In a recent report, Carballo-Rubio [1] utilizes the semi-classical theory of
gravity to obtain a generalized Tolman-Oppenheimer-Volkoff (TOV) equation. This
model has a new coupling constant $l_p$ implying two different modified TOV
equation forms characterized by the sign of $p'$. The negative branch reduces
to the ordinary GR-TOV in the limit of $l_p\to0$, while the positive one does
not. In the positive branch, Carballo-Rubio was able to find the exact
solutions using the constant-$\lambda$ trick. In this work, we investigate
whether this theory's negative branch can also provide a different feature of
the ultra-compact object compared to those obtained from the GR-TOV equation.
We study ultra-compact objects with an isotropically ideal fluid matter where
we use a simple but physically motivated equation of state $\rho=p/w+\rho_0$
with $w$=1 and $w$=1/3. In general, we obtain that the range of $l_p$ is very
restricted and must not be equal to $r_c$. Here $r_c$ is the starting point of
integration located at the center of the star. While $l_p$ should be set to be
much larger than Planck length $L_\text{Pl}$. Consequently, the mass-radius
curves for the various value of $l_p$ for both $w$ cases are still
indistinguishable from the standard GR-TOV results. Hence from the negative
branch of $p'(r)$, the additional free parameter $l_p$ does not provide a
significant effect compared to the standard GR-TOV equation results, even
though $l_p$ is not in the limit of $l_p\to0$ anymore. Therefore, similar to
the conclusion in Ref. [3] with GR theory that the ultra-compact objects from
negative branch of semi-classical gravity with a linear equation of state are
unable to generate demanding gravitational echoes.
