One of the all-time champions of brand-building, Nike (NYSE:NKE), delivered yet another solid quarterly performance to its investors Monday morning. Despite all the good news, though, there were a few notes of caution that make this Fool a bit concerned about the footwear industry.

Revenue for the first quarter rose about 8% over last year's level, and the company reported 32% higher net income as well. As you might imagine from those numbers, margins improved a bit for the quarter. Looking at other metrics, Nike reported that it generated about $197 million in free cash flow. Future orders climbed more than 11%, inventories rose by a similar amount, and the company bought roughly $151 million of stock in the open market.

While Nike is a quintessentially American brand, those who don't follow the company particularly closely might be surprised to learn that Nike generates almost as much revenue and income from Europe as from the United States. That said, European sales growth was a bit sluggish (roughly half of the growth seen in the U.S.), and I would imagine the state of the European economy is at least part of the problem. Elsewhere around the globe, Nike continues to grow strongly, with sales in Asia-Pacific up 10% in constant currency and in the Americas up 20% (also constant currency).

Listening to management's comments about the quarter, I hear some notes of caution. Despite a first quarter that surpassed analyst expectations, future guidance was muted. Although the company is looking for revenue to achieve the higher end of previous guidance, it now looks like there will be minimal gross margin expansion. What's more, the point was made that Nike generally separates itself from the pack when times get tougher and that such times may be on the way.

Frankly, that's not really news to our loyal readers. Shoe vendors like Foot Locker (NYSE:FL) and Finish Line (NASDAQ:FINL) have been reporting tough comps, and adidas apparently felt the need to get bigger and bought Motley Fool Stock Advisor pick Reebok (NYSE:RBK) to compete more effectively.

Now, nobody in his or her right mind thinks that the athletic/casual footwear business is going to evaporate, but it does seem as though almost everybody expects times to get tougher. With huge brand value, ample cash flow, and a sound balance sheet, investors may want to look at that scenario as a possible opportunity to get Nike shares a bit cheaper.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).