The carcass of the spotted deer was found from a field in Panahpur village, Divisional Forest Officer, South Kheri, Neeraj Kumar said.
He said injuries from some sharp edged weapons were detected on the carcass of the spotted deer, a protected species under the Wildlife Protection Act.
The deer had reportedly run away from a village in neighbouring Shahjahanpur district, following which he was chased and killed by the poachers, he said.
Being a protected species under schedule three of the Indian Wildlife Act, a case under section 9/51 of the act has been lodged against unidentified poachers while a probe has been ordered, Kumar added.
He was rushed to district hospital where his condition was reported to be critical.