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This bank just slashed its S&P earnings outlook to zero

The U.S. Federal Reserve is not the only one worried about global growth. Weakness in emerging markets is likely to weigh on the S&P 500's earnings potential according to Barclays, which has become the latest bank to downgrade its growth outlook for the U.S. index, warning that it now expects no growth at all for 2015.

A stronger U.S. dollar, sluggish global growth and emerging market headwinds are the main factors for Barclay's latest forecast, with the bank cutting its earnings per share (EPS) estimate for the S&P 500 to $117 from $123 for 2015.

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Traders work on the floor of the New York Stock Exchange.
Brendan McDermid | Reuters
Traders work on the floor of the New York Stock Exchange.

"The three primary consequences of trouble in emerging markets for U.S. equities are slower global growth, an appreciating U.S. dollar, and increased risk aversion. These should lead to lower earnings for the S&P 500 and more caution on sectors with large exposure to international markets, head of U.S. equity strategy at Barclays, Jonathan Glionna, said in a note to clients published late on Thursday after the Fed's decision to keep rates on hold.

Earnings per share (EPS) is a metric investors use to calculate the portion of a company's profits allocated to each share of common stock and generally points to level of a company's profitability.

"Our strategists believe any rebound in emerging markets could be difficult to sustain. This matters for the S&P 500. In other words, we now expect no EPS growth for the S&P 500 in 2015," Glionna added.

The bank also downgraded its outlook for the information technology sector to "market weight" from "overweight" due to its large exposure to overseas markets.

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"I think the problem that we have with the S&P is although the prices are lower and so there is bit more room for return, the multiples have been very stretched. The composition of that rise in the S&P, driven by defensives versus cyclicals was also quite extreme, so that is a characteristic of the market that is puzzling to investors," Francesco Garzarelli, co-head of European Macro at Goldman Sachs told CNBC.

Barclays' downgrade follows a cut from Goldman Sachs in July, which lowered its EPS outlook and S&P 500 year-end price forecast for both 2015 and 2016.

The investment bank also cited dollar strength and oil price concerns, lowering its 2015 EPS target by $8 to $114 from $122, or just 1 percent growth.

Despite the downgrades to earnings forecasts, both firms expect to see the index end the year at 2,100 up from current levels of around 1,990 as a later than expected Fed rate hike helps offset the earnings weakness.