Malvinder Singh is scrambling to play damage control over the US investigation into charges the generic drugmaker covered up a scheme to sell potentially adulterated meds, including AIDS pills. The news raised doubts about Daiichi Sankyo’s proposed $4.6 billion purchase of the Indian company, battering its stock.

But Singh maintains the investigation was disclosed to Daiichi as part of the due diligence process and blames an unnamed big pharma and another Indian drugmaker for spreading rumors in order to unravel the deal.

“There has been speculation in the market due to lack of understanding and we have information that a multinational and a leading Indian company are working in concert to bring our share price down. I have a clear sense of what is happening. People are trying to create confusion and obviously somebody is trying to bring our price down so that they buy Ranbaxy’s share at a lower price,” he tells The Hindu newspaper.

Meanwhile, as we noted last night, Congress now plans to conduct a probe.