A zero cycle path is a timing path that propagates from one flop to another racing the propagation of the same clock edge. This is a race condition. The RTL code must be modified to remove all zero cycle timing paths.
WHY: Zero cycle paths can only pass STA with manual intervention which is error-prone and re-quires Nuelight to document the zero cycle path and provide an exception file for STA when one exists within a RIP or bolt-on.
Check out the timing constraints for the specific Vendor software. You should have something for False path.
For Xilinx ISE, TIG - Timing Ignore is the timing constraint which is useful.
If you use this then, path will be ignored and you won't get any error for this.