external prescalar in PLL circuit

When I am using an external prescalar dividing VCO output in feed back path, to PLL chip, can I feed the prescalar output directly to PLL IC(Rfin port) or I must always use a attenuator pad in between to improve return los.

Ideally the output of the prescaler is 50 ohms, but in reality is not, so is good to use a pad for matching. Just check the available levels.