Investing.com - The S&P 500 is expected to fall as stocks face historically high levels of concentration, former JPMorgan Chase (NYSE: JPM ) chief market strategist Marko Kolanovic has told Bloomberg News.

Speaking with Bloomberg's "Odd Lots" podcast, Kolanovic, who abruptly left JPMorgan last July, warned that an imbalance between the influence of the ten biggest stocks in the market and other equities is not sustainable, adding that a cyclical downturn to "purge" sky-high valuations may be likely.

Prior to his departure from JPMorgan, Kolanovic had been a persistently vocal skeptic of a prolonged, multi-year stock market surge, warning in particular of potential headwinds from easing momentum in AI-powered mega-cap names that have underpinned the rally. Geopolitical tensions and a possible slowing in the U.S. economy were also seen by Kolanovic as risks.

Kolanovic has seemingly stuck to this bearish outlook, telling Bloomberg that he predicts the S&P 500, which entered Monday trading above 6,000 and touched a record high two weeks ago, could be "back down in the 5,000s this year". Potential turmoil under the new Trump administration could also bring index down "much lower into 4,000", Kolanovic told Bloomberg.

The comments come as recent events have pointed to some fragility in the stock market's long-standing push higher. Sweeping new tariffs from U.S. President Donald Trump announced over the weekend sent global stock markets roiling on Monday and pulled down U.S. stock futures.

Meanwhile, stocks sold off sharply last week after the emergence of a low-cost artificial intelligence model from Chinese start-up DeepSeek. The firm's claims that the model was both cheaper and required less-advanced data, although disputed, raised doubts over the necessity of massive AI spending strategies being pursued by mega-cap tech companies.

Markets have since recovered much of the losses posted during the DeepSeek-inspired decline, but Kolanovic flagged that the downturn is "perhaps not over", Bloomberg reported. He noted that he was especially keeping an eye on several more major corporate earnings due out in the coming days.