Bharti Airtel fell as much as 3.44% to its lowest intraday level since October 2008, after Credit Suisse downgraded the stock, citing the prospect Reliance Infotel would enter the wireless voice market.
The unit of Reliance Industries was expected to only enter the Indian wireless data market, but Credit Suisse said Reliance Infotel would benefit from also entering the voice market, increasing competition in a segment in which Bharti Airtel is one of the top players.
Credit Suisse cut its ratings on the stock to "underperform" from "neutral", while cutting its target price to 220 rupees.
Bharti's shares were last down 2.8% at 251.30 rupees.
Bharti has seen a slew of downgrades including Morgan Stanley, Goldman Sachs, Standard Chartered following disappointing quarterly earnings.