  Recent measurements carried out at comet 67P/C-G with the ${\it Rosetta}$
probe revealed that molecular oxygen, O$_2$, is the fourth most abundant
molecule in comets. Models show that O$_2$ is likely of primordial nature,
coming from the interstellar cloud from which our Solar System was formed.
However, gaseous O$_2$ is an elusive molecule in the interstellar medium with
only one detection towards quiescent molecular clouds, in the $\rho$ Oph A
core. We perform a deep search for molecular oxygen, through the $2_1 - 0_1$
rotational transition at 234 GHz of its $^{16}$O$^{18}$O isotopologue, towards
the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293--2422
B with the ALMA interferometer. The targeted $^{16}$O$^{18}$O transition is
surrounded by two brighter transitions at $\pm 1$ km s$^{-1}$ relative to the
expected $^{16}$O$^{18}$O transition frequency. After subtraction of these two
transitions, residual emission at a 3$\sigma$ level remains, but with a
velocity offset of $0.3 - 0.5$ km s$^{-1}$ relative to the source velocity,
rendering the detection "tentative". We derive the O$_2$ column density for two
excitation temperatures $T_{\rm ex}$ of 125 and 300 K, as indicated by other
molecules, in order to compare the O$_2$ abundance between IRAS16293 and comet
67P/C-G. Assuming that $^{16}$O$^{18}$O is not detected and using methanol
CH$_3$OH as a reference species, we obtain a [O$_2$]/[CH$_3$OH] abundance ratio
lower than $2-5$, depending on the assumed $T_{\rm ex}$, a three to four times
lower abundance than the [O$_2$]/[CH$_3$OH] ratio of $5-15$ found in comet
67P/C-G. Such a low O$_2$ abundance could be explained by the lower temperature
of the dense cloud precursor of IRAS16293 with respect to the one at the origin
of our Solar System that prevented an efficient formation of O$_2$ in
interstellar ices.
