The female fox was discovered by a member of the general public in a collapsed state in a garden in Buxton Road, Spixworth.
RSPCA animal rescue officer David Allen participated in the occurrence on December 26 and took the fox to East Winch Wildlife Centre for immediate treatment.
The fox was offered fluids for 24 hr and prior to being offered basic prescription antibiotics and a regular dewormer.
She was launched back to the wild by the RSPCA on January 26.
Blood tests were undetermined of poisoning.
Mr Allen said: “While we cannot be specific it is toxin, the fox was showing behavioural indications of poisoning.
“What is suspicious and worrying for us is that the caller said that there have actually been other suspicious fox deaths in the neighboring meadow location over the last number of years.
“We are keen to speak to anyone with first-hand knowledge of this so we can look into it further.”
Anyone with info needs to call the RSPCA’s appeals line on 0300 123 8018.