For investors in the S&P 500 (SNPINDEX:^GSPC), April brought modest but solid gains, with the index rising 0.6% and hitting an unprecedented high-water mark. However, many stocks missed the boat, especially as investors punished momentum stocks that had produced the biggest gains over the past year. But several stocks did poorly during the month, raising questions about whether they'll be able to deliver future gains for shareholders. Let's take a closer look at Intuitive Surgical (NASDAQ:ISRG), Under Armour (NYSE:UAA), and Xilinx (NASDAQ:XLNX) to find out why they topped the list with losses of worse than 10%.

Source: Intuitive Surgical.

Intuitive Surgical dropped more than 17%, with two major drops pulling the stock down during April. Early in the month, the robotic surgery specialist warned that its first-quarter results would come in weaker than investors expected, with overall revenue falling 24% on a particularly bad 60% drop in revenue from da Vinci system sales. Then, when Intuitive Surgical actually reported its results, shares took another hit, as Intuitive Surgical's guidance for the remainder of the year caused further disappointment. The big question going forward for Intuitive Surgical is whether reluctant buyers who've been evaluating major changes in the health-care industry will finally start buying da Vinci systems again, or whether the price tag for major capital expenditures will remain too high. A recovery in system sales would be all Intuitive Surgical needs to regain its losses.

Source: Under Armour.

Under Armour fell almost 15%, with most of the damage coming after the athletic apparel maker's first-quarter earnings report. Even though sales rose 36% from year-ago levels, leading to a 71% jump in earnings per share, Under Armour still didn't deliver the forward guidance that investors wanted to see. Admittedly, the stock's high valuation has made some investors nervous. But the long-term growth story at Under Armour appears intact, and when a company raises guidance, sending shares downward seems like an overreaction.

Xilinx dropped 13% after the chipmaker missed earnings expectations. Xilinx said that with weak demand from the aerospace, defense, and wireline telecom industries, the company would see order declines in the current quarter. Yet the longer-term question is whether Xilinx's key customers will bounce back in the remainder of the year and beyond. In particular, with demand for commercial aircraft soaring, Xilinx has an opportunity to bounce back if major producers start bulking up their orders again.

Of these stocks, Under Armour has the best chance for a quick rebound, if investors realize that the company's growth potential still exists. For Xilinx and Intuitive Surgical, it might take longer to persuade shareholders in their turnaround stories, although all three stocks could be good values if they can get back on track with their respective businesses.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.