Protecting analog inputs when BBB is powered down

I need to protect a BBB's analog inputs when it's powered down. I
don't need protection against overvoltage when working as the circuit
connected to the ADC input will only have a maximum of 1.3 volts
applied (a single NiMh cell).

However it's possible/likely that the single cell will be there when
the BBB is powered down. So how can I protect the ADC inputs? Would
a series resistor plus a diode clamp to the ADC +ve reference be OK?
The series resistor can be quite large because the ADC inputs take a
really tiny current.

I want this to be really simple so would prefer to avoid any logic
driven by the reset line and such.

On another system I already use very low power op-amps supplied from
the AD +ve reference and that works fine so I'm wondering if the above
resistor + diode will be satisfactory too.