The striker squandered two clear-cut opportunities in the goalless Group B draw in Port Elizabeth that came as a blow to the Congolese hopes of reaching the quarter-finals.
Anderlecht's Mbokani had been up late the night before participating in Belgium's televised annual football award ceremony, where he was named the best player in the league.
He accepted the award in a satellite link from next to the swimming pool at the team hotel on Wednesday.
"Maybe we lost concentration with this party," said Le Roy, whose side must now beat Mali in Durban on Monday to progress to the last eight.
"It was a difficult decision for me to make because it is such an important award for Mbokani, the first time he has won it. I could not stop him from receiving the award because that would have cut him on a mental level. It's such a big moment in his career.
"Belgian television respected everything they promised me but it finished around 11.30pm. It's no excuse at all but it might be a reason why we lost concentration in the game."
Mbokani was twice clear on goal in the first half but watched in horror as his efforts went too close to goalkeeper Daouda Kassaly. He was largely ineffectual in the second half at the Nelson Mandela Bay Stadium.
The 27-year-old Mbokani moved from Congo to Belgium, the country's former colonial power, in 2006 and has two separate spells at Anderlecht and also played at Standard Liege, Monaco in France and Bundesliga club VfL Wolfsburg.
Congo has been a steady supplier of talent to the Belgian league but Mbokani is the first Congolese to win the award since its inception in 1954.
- Sports & Recreation