Dagdoug, 24, was tested after Esperance played Al-Merrikh of Sudan in the first round of the group stage on Feb. 11, a match in which the left-back was an unused substitute.
Esperance of Tunisia defender Houssem Dagdoug has tested positive for an unspecified banned substance after a CAF Champions League match last month, the club confirmed on Friday.
Dagdoug, 24, was tested after Esperance played Al-Merrikh of Sudan in the first round of the group stage on Feb. 11, a match in which the left-back was an unused substitute.
He then played in two other group games.
Esperance said on their website that the Confederation of African Football (CAF) had informed them of Dagdoug's failed test and that they were awaiting further details in the case.
The club added that CAF had not yet informed them of the consequences for Dagdoug.
Esperance are currently at the top of Group D in the Champions League with nine points, three ahead of Algeria's CR Belouizdad.
Egyptian side Zamalek are in third place, level on four points with Al-Merrikh in fourth.
Dagdoug, who joined Esperance in 2020 from Club Africain, has made 16 appearances for the club this season.
He will now face a ban and the length of his suspension will be determined by the type of substance he tested positive for.
Dagdoug is the second Esperance player to suffer such fate after former forward Taha Yassine Khenissi was suspended by CAF for a year after violating anti-doping rules.
Khenissi tested positive for a WADA prohibited substance during their Caf Champions League match against MC Alger on May 10, 2021.