The S&P 500 and FTSE 100 could plummet further if key resistance levels aren't held, Phil Roberts, technical analyst from Barclays Capital, told CNBC.
If the S&P 500 can't close above 986 and if the FTSE doesn't close above 4,347 then "the mayhem could still continue," Roberts told "European Closing Bell."
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The FTSE has enjoyed three consecutive sessions of gains this week, giving some investors hope for calmer markets ahead. But the VIX volatility index is still trending higher.
"If we are coming into a period of stability then the VIX has got to reverse this uptrend," Roberts said. "There are signs it is losing momentum, but it's still above the 21-day moving average (around 62.5) … It's still behaving like it wants to go higher," he added.
Roberts is also bearish on the euro versus the dollar and predicts the currency cross could fall to 1.15 / 1.20.