The eclipsing X-ray binary M33 X $ - $ 7 was in the field of view during several observations of our XMM-Newton M33 survey and in the archival Chandra observation 1730 which cover a large part of the 3.45 d orbital period .
We detect emission of M33 X $ - $ 7 during eclipse and a soft X-ray spectrum of the source out of eclipse that can best be described by bremsstrahlung or disk blackbody models .
No significant regular pulsations of the source in the range 0.25–1000 s were found .
The average source luminosity out of eclipse is 5 \times 10 ^ { 37 } erg s ^ { -1 } ( 0.5–4.5 keV ) .
In a special analysis of DIRECT observations we identify as optical counterpart a B0I to O7I star of 18.89 mag in V which shows the ellipsoidal heating light curve of a high mass X-ray binary with the M33 X $ - $ 7 binary period .
The location of the X-ray eclipse and the optical minima allow us to determine an improved binary period and ephemeris of mid-eclipse as HJD ( 245 1760.61 \pm 0.09 ) \pm N \times ( 3.45376 \pm 0.00021 ) .
The mass of the compact object derived from orbital parameters and the optical companion mass , the lack of pulsations , and the X-ray spectrum of M33 X $ - $ 7 may indicate that the compact object in the system is a black hole . M33 X $ - $ 7 would be the first detected eclipsing high mass black hole X-ray binary .