Independent trading houses in the $9.6 trillion-per-day foreign exchange market face an uphill battle to grab share from more established banks, according to a new report.

These so-called nonbank liquidity providers — think high-frequency market makers and other specialists — have steadily grown their footprint in currency trading over the last two decades. Last year, they minted some $2 billion in profit, but a bevy of factors are likely to limit their growth, financial services consulting firm Crisil Coalition Greenwich said Tuesday.