Alcoa slashes China production forecast; Yum Brands, Nu Skin outlook for China sours in less than two months China is fast becoming a major source of worry for the stock market again, after commentary from a number of U.S. companies this week warned that demand from the second-largest economy may have dropped sharply over the past month. That doesn’t bode well for the third-quarter earnings reporting season, which was already expected to be the worst quarter for U.S. companies in six years. Worries about a slowdown in China aren’t new. The more than 40% tumble in the Shanghai Composite stock index SHCOMP, +0.17% and the devaluation of the yuan over the summer helped fuel the selloff on Wall Street in late August, when the S&P 500 index entered correction territory for the first time in about three years. But those worries had been soothed somewhat, after the Chinese market stabilized in September, and following upbeat comments from some U.S. companies about how business in the country had improved. Nike Inc. NKE, +1.19% helped spark some of that optimism in late September, after the blue-chip athletic apparel and accessories giant reported a 30% jump in sales in Greater China in its fiscal first quarter, which ended Aug. 31. But dire outlooks on China from Alcoa Inc. AA, -1.75% Yum Brands Inc.YUM, +0.84% and Nu Skin Enterprises Inc. NUS, -0.14% this week could wipe away that optimism, especially considering how sudden the companies’ outlooks soured. FactSet Alcoa unofficially kicked off earnings reporting season late Thursday, missing profit and sales expectations for the third quarter ended Sept. 30. The aluminum giant slashed its 2015 growth outlook for automotive production and commercial building and construction sales in China, and said heavy duty truck and trailer production would fall much more than previously expected. In July, Alcoa didn’t break out its outlook for China. Yum Brands’ stock tumbled to a one-year low this week after the fast-food restaurant operator reported third-quarter profit and sales that missed expectations, as “unexpected headwinds” led to disappointing results out of China. Revenue from China represented 52% of the company’s total over the last 12 months, according to FactSet. This was a big surprise to investors, because as recently as Aug. 18, Yum Brands Chief Executive Greg Creed said, “same-store sales have turned significantly positive” in China. Some of Yum’s China woes could be viewed as company specific, as the company struggles to get past food-safety concerns that surfaced nearly three years ago. But in a conference call with analysts Wednesday morning, Yum executives highlighted the “macro softening” in China’s economy, as well as currency pressures and increasing competition, according to a transcript provided by FactSet. Nu Skin shares plunged to a near three-year low this week after the cosmetics company lowered its third-quarter revenue outlook because of disappointing sales in China during August and September. Just two months earlier, Nu Skin said it was “particularly” pleased with progress in mainland China, where it generated “healthy sequential growth in both sales leaders and revenue.” China accounted for 26% of Nu Skin’s total revenue over the last year, according to FactSet. Keep in mind that while Nike’s upbeat outlook on China was for the quarter ending August, China troubles for Alcoa, Yum and Nu Skin were for the quarter ending September. This suggests the outlook for China may have fallen off a cliff in September, which warns that third-quarter earnings for the S&P 500 could end up being worse than feared. As of Friday, aggregate earnings per share are expected to drop 5.5% from a year ago, which would be the worst quarterly performance since the third quarter of 2009. Read more about the outlook for third-quarter earnings. As of June 30, earnings were expected to decline just 0.9%. FactSet Among some of the larger companies scheduled to report over the next week, 19.4% of Intel Corp.’s INTC, +0.22% revenue over the last 12 months came from China, just behind the 20.7% from Singapore, and ahead of the 17.6% from the U.S., according to FactSet. Intel is scheduled to report third-quarter results on Oct. 13. Read more about which companies and sectors have the most exposure to China. FactSetChina’s outlook a big deal for Intel Also reporting next Tuesday, China accounted for 7% of Johnson & Johnson’sJNJ, +0.65% revenue over the last 12 months, and for 2.7% of J.P. Morgan Chase & Co.’s JPM, -0.34% revenue, according to FactSet. The key to China’s impact on earnings season could come next Wednesday, when Nike holds its investor day. Any hint that sales to mainland China, which accounted for 9.2% of Nike’s total sales, slowed since the end of August would not bode well for overall corporate earnings, and in turn the stock market. More from MarketWatch