The Cairn India stock fell 5.56 per cent to Rs 170.60 - its 52-week low - on BSE.
On NSE, it was down 5.69 per cent at Rs 170.55.
Shares of Vedanta, however, rose 4.15 per cent to Rs 184.40 on BSE.
According to news reports, Vedanta is in final stages to announce merger of Cairn India, a listed oil and gas explorer, with itself.
The move may give the parent access to Cairn's cash and help reduce debt, the reports said.