A Donald Trump win could spark an immediate sell-off of up to 5 percent for the S&P 500 (INDEX: .SPX), according to analysts at Citi, who also warn on slower growth or even recession for the U.S.

A survey run in September by the U.S. investment bank showed Wall Street strongly believes Hillary Clinton is set to clinch victory in next week's vote but the poor performance of U.S. equity markets in the wake of last Friday's news of the latest FBI probe into the Democratic candidate's emails, shows concerns of a Trump win are mounting.

According to the latest note out from global equity strategists at Citi Friday, fears for stocks after a Trump victory are two-fold.

In the longer-term says the research team, "A Trump win risks slower growth or recession if trade is restricted and fiscal expansion plans curtailed. Uncertainty alone could hit the economy. Global growth will also be impacted if uncertainty rises, U.S. growth is hit and U.S. financial conditions tighten."

Yet even in the immediate aftermath of the vote, markets could drop, according to Tobias Levkovich, the chief U.S. equity strategist at Citi.

"If Donald Trump were to win, that outcome would have been unexpected and thereby may cause a jump in the equity risk premium with negative P/E (price –to-earnings) multiple repercussions. We think a Trump victory could spark a 3-5 percent setback in the S&P 500," summarizes the Citi note.

The price-to-earnings ratio is a key valuation metric for stocks which gauges how much an investor must pay on the stock market for each cent of earnings.

The overwhelming majority of commentators also see the same trajectory for the S&P 500, with analysts at Barclays warning markets could drop between 11 and 13 percent in the case of a Trump win as opposed to a 2 to 3 percent bounce if Clinton emerges victorious.

However, in a New York Times article on Monday, Lawrence G. McDonald of ACG Analytics reportedly suggested there was a silver lining to all the current apprehension and negativity.

According to McDonald, "Trump will create a colossal panic, but the relief rally will be outstanding."

"Trump's bark found in his anti-globalization position in reality will be a lot worse than its bite in terms of actual implementation," he continued.

While overall U.S. equity markets may take a pummeling if analyst expectations materialize, some sectors would be likely beneficiaries if Trump moves into the White House.

According to the Citi note, one example is certain energy subsectors, particularly those confronted by environmental challenges.

"The energy sector, coal mining, possibly chemical manufacturers and utilities would do better under less environmental scrutiny versus a Clinton win, which would be better for more environmentally friendly firms."

However, other energy subsectors may actually prefer the opposite outcome.

"A Clinton victory might pressure the oil and gas industry via more restrictions on drilling but that would also support oil prices and help the Energy sector," explained the note.

Similarly, Clinton's vow to investigate what she sees as many examples of egregious pricing for medication means some health care stocks could expect to do better out of a Trump victory.

However, Citi believes the case in health care is not quite so clear cut.

"We suspect that both nominees have a negative perspective on the health care industry, with Clinton having a long-term issue with drug pricing. Trump's populist tone may be even worse as he discusses tearing up 'Obamacare' and replacing it with some unknown program."

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