It may be a fuse but its unlikely, can you provide me with the model of Zanussi oven.
So I am clear on the fault you have a grill element which outer and inner ring, the inner element works but the outer one doesnt, and this is after you have replaced the element.
If the above is correct the first thing to do is use a multi meter to check your getting power to the element (which its unlikely you are), then do a continuity check on the fuse which should be fine, work your way back to the control knob and check your getting a power. My guess is its the control knob which is at fault, but by using a multi meter this will prove the fault before you need to order any spares.
I cant see where the fuse is on the parts diagram (see attached), that said please let me know how you get on checking the circuit with your multi meter, but from what you have said I still think the fault is likely to be with the control switch.