It said India will have to address issues plaguing private investment, and banks will have to clean up their balance sheets, it said, adding the country lacks infrastructure.
"India has edged out China as the world's fastest-growing large economy, despite a slowdown in global growth and tough times for many emerging markets. However, this outperformance could prove temporary if India's reforms do not gather greater momentum," the US-based agency said in a statement.
S&P said the recent trend of strong economic growth in India could slow in the medium term if improvements in the country's infrastructure do not pick up.
A heavy debt burden and relatively large fiscal deficits prevent heavier budgetary spending to ease this constraint. Past attempts at allowing the private sector a role in infrastructure have met with limited success due to legal and bureaucratic obstacles, it said.
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But the ability to deploy monetary and fiscal stimulus is limited by the absence of fiscal cushion and inflation dynamics.
"India will have to address issues plaguing private investment and banks will have to clean up their balance sheets. Companies in infrastructure and other asset-heavy sectors will also need to deleverage materially," it added.
A broad-based revival in investment, with the corporate sector playing a key role, is critical for attaining and sustaining India's economic growth trajectory, Crisil chief economist Dharmakirti Joshi said.
India's infrastructure remains lacking by many measures and improvements are being made only gradually.
"It also lags significantly behind that in neighbour China in most aspects. India's weak fiscal metrics are a reason the infrastructure gap between the two Asian giants exists," Tan said.
Increasing budgetary allocation to public capital spending remains the most likely way to speed up infrastructure building in the near term, S&P said, as it cautioned against raising taxes without structural reforms as it would dampen business sentiment.
In addition, income tax collections have slowed significantly in recent years due to economic uncertainties. Consequently, more spending on infrastructure most likely means less spending elsewhere, it said, adding among the major budgeted expenditures, spending on subsidies has the most potential for reduction.
"Without permanent cuts to some of these programs, the government will find it difficult to raise capital spending, and India's economic growth may have to glide lower over time," he added.