He said that Prime Minister Narendra Modi, BJP president Amit Shah and Chief Ministers of all BJP and NDA-ruled states will participate in the oath taking ceremony in Lucknow on Sunday.
Senior JD (U) leader KC Tyagi also raised similar apprehensions, saying, "The appointment of Yogi Adityanath as the chief minister would further polarise the state".
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A five-time MP from the BJP, Adityanath is a popular leader known for his fiery Hindu rhetoric who has stirred controversies over his polarising and inflammatory speeches against Muslims - who form almost 20 percent of the state's population.
Earlier today, Adityanath was summoned to Delhi on a special flight to meet Prime Minister Modi, but he returned to Lucknow without being able to meet the PM Modi.
He is not known to enjoy good rapport with the BJP leadership and his elevation has left many puzzled, with political circles abuzz with talk of RSS having prevailed over the party in deciding the new chief minister.
The BJP had a landslide victory in UP this month when they secured 312 seats in the 2017 assembly polls..
His supporters believe that Adityanath, who is a strong votary of construction of a Ram temple at the disputed site in Ayodhya, drove BJP's Hindutva campaign single-handedly in eastern UP.
The yogi then launched the Hindu Yuva Vahini, which helped him establish his dominance over the region.
While the BJP MP has largely focused on Hindutva, one can not overlook his contributions to the development cause either.
"These discussions are futile and unnecessary", Rajnath told ANI when asked about him being in the race for becoming UP Chief Minister.
Opposition leaders took to Twitter to express their views.
Before announcing Adityanath as the CM, the party was set to give Union Minister Manoj Sinha the charge of UP, as per reports.
Interestingly, the newly appointed Uttarakhand chief minister, Trivendra Singh Rawat, is also from the same community. Leaders of two allies of the BJP -Apna Dal (Sonelal) chief and Union minister Anupriya Patel and Suheldeo Bhartiya Samaj Party chief Om Prakash Rajbhar were also present in the meeting.