Foreign inflows into Indian bonds will reach a decade-high of $2 billion around June 28, when they will be included in a widely followed JPMorgan index, but the central bank will absorb the majority of the dollars to prevent a sharp surge in the rupee, bankers said. The $2 billion single-day inflow estimate by four bankers trails only the record-breaking $2.7 billion poured into Indian bonds on August 20, 2014, as hopes of a credit rating upgrade grew.

More than $200 billion in assets follow the JPMorgan Emerging Market Index, in which India will eventually have a 10% weight by March 2025, implying total passive inflows of at least $20 billion over the 10-month timeframe.

The Reserve Bank of India, which has been keeping a close eye on the rupee to prevent it from falling to lifetime lows, will monitor inflows and speculative posture on the currency, but has not implemented further surveillance measures, according to a source familiar with the RBI's intentions.

"It's just a case of inflows, this time in debt instead of equities," said a source. "It might be positive for the rupee and might be positive for FX reserves as well."

The source and bankers requested anonymity since they are not permitted to speak to the media. The RBI did not immediately respond to an email requesting comment.

The RBI is apprehensive of any considerable strengthening of the rupee because its actual effective exchange rate, which measures its relative worth against a basket of currencies, indicates that it is modestly overvalued, according to the source. While anticipating the inflows may strengthen the rupee, a significant gain is unlikely given the central bank's control over the currency, bankers said.

The RBI has stated that it will continue to increase its forex reserves opportunistically, avoiding a precipitous jump in the rupee. Because there is no precedent for these debt index-related inflows, bankers' predictions of flow timing are based on comparable index revisions in the equities markets.