French sports daily L'Equipe reports on its website that Laalou was sent home from the Olympics after a banned diuretic was found in a sample he gave at the Monaco Diamond League meeting last month.
Laalou was scheduled to run in the 1,500 heats Friday evening. He reached the semifinals at two previous Summer Games.
The 30-year-old runner reportedly tested positive for furosemide, which can be used to disguise the presence of other banned drugs.
Athletics' governing body, the IAAF, declined comment on the reports.
The IAAF suspended another Moroccan 1,500 runner, Mariem Alaoui Selsouli, after she tested positive for furosemide last month.Suggest a correction