  XRF 030723 is the first X-ray flash (XRF) to show in its optical light curve
(LC) a bump that has been interpreted as the signature of a supernova (SN).
After subtracting the afterglow component from the observed optical LC of the
XRF counterpart, the properties of the putative SN are constrained by means of
synthetic LCs of core-collapse SNe. For the redshift range $z \sim 0.3$ -- 1,
all possible models require a rather small mass of synthesized \Nifs, i.e.
$M$(\Nifs) $\sim$ 0.01 -- 0.3 $\Msun$. The models used to describe the
energetic SNe Ic associated with gamma-ray bursts (SNe 1998bw and 2003dh) are
too massive for the observed LC. If the relation between ejected \Nifs mass and
total ejecta mass established from models of various Type Ic SNe also holds for
the putative SN in XRF 030723, the ejecta mass is constrained to be $\sim$ 1 --
3 $\Msun$ and the kinetic energy $\lsim 1\times 10^{52}$ erg. This corresponds
to a progenitor with $15\Msun \lesssim M_{\rm MS}\lesssim 25\Msun$. The SN
therefore appears to have properties intermediate between a normal SN Ic like
SN 1994I and a more energetic object like SN 2002ap.
