Earlier Pramod Patel was fielded by the ruling party from Pratapgarh.
"The party has replaced Pramod Patel, and C N Singh will be party's candidate from Pratapgarh constituency," SP national general secretary, Ramgopal Yadav said in a release issued here.
The party has also declared Shivendra Singh as its candidate for by-election to Rampur Khas Assembly seat in Pratapgarh. The seat had fell vacant due to resignation of Congress MLA Pramod Tiwari, who was elected to Rajya Sabha.