NEW DELHI—India’s economic growth is expected to have slowed last quarter, hurt by weak industrial and agricultural output, raising concern that the recovery of Asia’s third-largest economy is already losing steam.

Gross domestic product in the three months ended Sept. 30 likely grew 5.1% from a year earlier, according to the median estimate in a poll of 16 economists by The Wall Street Journal. If the forecast is correct, that would be a significant step down from the 5.7% expansion in the preceding quarter.

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