Officers are understood to have dismissed Mohammed Saeed Zao as a "trouble-maker" after the assassination bid on Friday night.
Middle East Concern, a group trying to defend the religious freedoms of Christians, said: "Please pray for Mohammed's protection, that there will be no further attempts to kill him now that the police have refused to deal with the case."
Zao, who is well-known for his promotion of the rights of Christians and has made many media appearances, was approached by a man who tried to stab him.
The suspect came out from of a nearby car carrying a long knife or sword and targeted Zao as he returned to his Casablanca apartment.
Zao was able to protect himself by opening an entrance door and, according to one newspaper, the suspect hurled threats at him before leaving the scene.
Christians are being urged by Middle East Concern to pray "that Mohammed will know the comfort of Jesus and the wisdom of the Holy Spirit as he tries to deal with the situation."
The organisation added: "Please pray for religious freedom in Morocco [and] for unity throughout the Christian community in Morocco, and good co-operation between the different churches in the country."