There was speculation on social media that the 40-year-old actor could throw his weight behind a candidate of another party.
Election officials said the actor's nomination papers only had "valid" signatures of eight proposers, not the mandatory 10.
On Thursday, Vishal said the two people who had reportedly proposed his nomination for the RK Nagar by-poll are under threat from Tamil Nadu's ruling AIADMK. "I am worried about those two people who signed up for me. We are not able to get in touch with them," he told NDTV.
The AIADMK has fielded a senior leader, E Madhusudanan, who has held the seat before and has influence among Telugu people who have a sizeable presence in RK Nagar.
Vishal's star power and Telugu roots are being seen as a direct threat to prospects of AIADMK's candidate Madhusudanan, who too, many insiders say, banks on the community's support. But the party denies the actor's allegations. Ma Foi Pandiarajan, Tamil Culture Minister, said "All those allegations are untrue."
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