Semiconductor giant Nvidia (NVDA) experienced a further decline in its stock price today, following a down session on Thursday. This decline comes after concerns raised by Paul Wick, a seasoned fund manager at Seligman Investments, who reduced his exposure to the stock.

Speaking at a UBS Group event, Wick expressed serious doubts about Nvidia's ability to sustain earnings growth. He underscored the company's high customer concentration as a significant risk factor. Unlike competitors like Microsoft (MSFT) and Alphabet (GOOG, GOOGL) with a broader customer base, Nvidia relies heavily on its top 10 clients for a significant portion of its revenue – estimated to be between 60% to 70%.

"This exposure makes Nvidia inherently a much riskier company than Microsoft or Google, who have very low customer concentration and thousands of customers," Wick said, according to Bloomberg News.

Adding to his concerns, Wick also raised doubts about Nvidia's current valuation. The stock is nowadays trading at a price-to-earnings ratio of 50, according to Yahoo Finance data. Wick questions the sustainability of this valuation, particularly considering that generative AI companies, major consumers of Nvidia's GPUs, are not showing strong returns on investment. Moreover, the potential development of in-house processors by some of Nvidia's top clients could significantly impact the company's future prospects, further adding to the uncertainty.

Despite his concerns, it's worth noting that Wick's stance on Nvidia is not entirely negative. According to StreetInsider, Nvidia remains one of Seligman Investments' top holdings, indicating that Wick still sees potential in the company despite the risks he has identified.