Dirar's side are preparing to embark on a UEFA Champions League quarter-final against Juventus starting Tuesday, while Monaco remain in the hunt for the French top flight title too.
Meanwhile, Falcao - on loan at Manchester United - looks set to go trophy-less in his first season at Old Trafford.
Dirar said while Monaco have missed the services of Falcao and James Rodriguez (Real Madrid), the Morocco international felt those who departed would be ruing the chance at glory under coach Leonardo Jardim.
"We talk all the time with Falcao and James, but there was also Mounir [Obbadi] and Manu [Riviere] who left. All these players we have missed. Early in the season, we took a slap, it was hard," Dirar told Le Parisien.
"I think Falcao must be biting his fingers [ruing the fact] he's gone. Here, he would have played and participated in the Champions League. But he may need more atmosphere.
"In Monaco, he was not feeling well."
