Global investors could pull more than $2 billion from Indonesian equities in the coming months if MSCI Inc. moves ahead with proposed changes to its indexing methodology, raising fresh concerns over the investability of Southeast Asia’s largest stock market.

The index provider is set to decide by the end of January whether to tighten its definition of free float — the proportion of shares available for trading, which plays a critical role in determining a stock’s index weighting — after gathering feedback from market participants. Should the changes be approved, they would take effect during MSCI’s May index review, potentially triggering sizable portfolio rebalancing by global funds.