October ended with a thud for investors as disappointing earnings from Microsoft and Meta Platforms pushed the indexes down on the last day of the month, and an accounting scandal at AI server maker Super Micro Computer weighed on AI stocks.

As you can see from the chart below, the indexes sank into negative territory on the last day of the month.

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Market pullbacks can sometimes create buying opportunities, so let's take a look at the three worst-performing stocks in October to see if any of these blue chips are worth buying.

1. Nike (down 12.8%)

Nike's (NYSE: NKE) woes continued last month as the sportswear giant posted another quarter of disappointing results. It's losing market share to upstart rivals and trying to fix the mistakes that took place under former CEO John Donahoe.

Nike axed its CEO in September, bringing in longtime company veteran Elliott Hill to run the company. With revenue and profits falling by double-digits, Nike has a lot of work to stabilize the business and get back to growth. But Hill seems like a good choice for the job as he's run Nike's product and marketplace division, and should be able to help restore some of its historical strengths.

That includes rebuilding its wholesale business, which the company deprioritized to focus on its direct-to-consumer business. Ignoring wholesale customers gave an opportunity to its competitors. Nike could also use a product refresh, as it has relied too much on classic styles to drive sales.

Overall, there is comeback potential for the stock, but I'd like to see evidence that it's starting to gain traction before calling it a buy.

2. Merck (down 9.9%)

Pharmaceutical company Merck (NYSE: MRK) was another underperformer on the Dow last month. The stock fell steadily throughout October as rising interest rates pressured dividend stocks like Merck, which pays a dividend yield of 2.9%.

Merck delivered a solid earnings report at the end of the month, but the stock still fell on the news. Revenue in the quarter rose 4% to $16.7 billion, which was ahead of the consensus at $16.46 billion.

Sales were again driven by Keytruda, its drug that helps the immune system fight cancer, which was up 17% to $7.4 billion, making up nearly half of Merck's revenue. On the bottom line, the company reported adjusted earnings per share of $1.57, which beat estimates at $1.50.

Animal health sales were up 6%, but Merck's other drug franchises declined, including Gardasil, ProQuad, and Januvia, and the company's concentration risk is now mounting as Keytruda approaches half of its sales.