It's been a rough period for many top stocks lately. High inflation and concerns that the extremely contagious Delta variant could usher in new waves of coronavirus lockdowns around the globe continue to fuel investor anxiety about another potential market crash. The good news is, there are plenty of quality stock-buying opportunities for long-term investors to seize upon.

Whether a few weeks from now or a few months out, it's highly possible that another downturn could be nearing. Given that possibility, now is an excellent time to fortify your portfolio with more high-caliber stocks that can drive sustainable long-term returns and help your holdings stay afloat if things get rocky again.

Here are two resilient stocks to buy before that happens.

happy person in colorful disco outfit dancing against purple background

Image source: Getty Images.

1. Teladoc

Teladoc (TDOC -2.91%) is one of the world's largest providers of telehealth services and is continuing to grow its business at an astonishing pace. The company's platform draws patients and medical providers from around the globe with services that bridge the full range of healthcare needs -- from general medical visits to wellness care to online therapy.

Teladoc's dual acquisitions of fellow virtual-care company InTouch Health and applied signals giant Livongo in 2020 have enabled it to tap into millions of new potential users. At the same time, the company offers a comprehensive healthcare experience at a scale no competitor has yet come close to rivaling.

In Teladoc's most recent quarter, the company reported that its revenue increased 151% on a year-over-year basis. In the U.S., Teladoc's paid memberships rose 20% during the first quarter, while users paying per-visit fees to access the platform surged 15% from the year-ago period. And total worldwide visits on Teladoc's platform popped by nearly 60% year over year during the three-month window.

The company reported 98% revenue growth in 2020 and is expecting to generate more than 80% revenue growth in 2021.

Bear in mind, the global digital healthcare market is expanding at an incredibly rapid place. This industry was valued at just over $61 billion in 2019, according to Fortune Business Insights, but is set to achieve a global valuation of $559.5 billion as of 2027.

Shares of Teladoc have taken a beating over the past few months, but this just creates an exciting opportunity for shrewd, long-term investors to snap up this compelling healthcare stock at a bargain price. While shares of the company are trading down 22% year to date at the time of this writing, the stock has still gained an eye-popping 912% over the past five years.

With top analysts estimating that Teladoc has a potential upside of more than 90%, the stock has plenty of growth left that new and existing shareholders can leverage into long-term portfolio gains.

2. MercadoLibre

E-commerce and fintech are two highly lucrative sectors that have seen exceptional growth in recent years and have flourished since the start of the pandemic. If it sounds intriguing to invest in both sectors through a single stock, MercadoLibre (MELI -0.45%) just might be the one for you.

MercadoLibre is the largest e-commerce platform in Latin America. This is no small feat. According to Statista, e-commerce sales in Latin America hit the $70 billion mark in 2019 and are on track to reach $116 billion by 2023. The other side of MercadoLibre's business is its payments ecosystem, which generated 75% total payment volume growth in 2020 alone.

In 2020, MercadoLibre reported that its net revenues spiked by a grand total of 73%, and its gross profits increased 55% from the prior year.

MercadoLibre was off to a roaring start in the first quarter of 2021. Management reported that the company's net revenues increased 158% from the year-ago period, and gross profits surged 89%. During the three-month stretch, MercadoLibre's total payment volume rose 129%, and the total payment transactions conducted on its platform surged 116% year over year. In addition, its gross merchandise volume popped 114% from the year-ago period.

MercadoLibre was founded in 1999, but it didn't become a publicly traded company until 2007. If you had invested $10,000 at the time of the company's initial public offering (IPO), when it debuted for a mere $18 per share, that initial investment would be worth just shy of $847,000 today. Meanwhile, the stock is up about 55% from where it was trading just one year ago.

Even with MercadoLibre's remarkable share-price growth, analysts still think the stock has an upside potential of more than 60%. They are also projecting that the company can hit consistent double-digit average annual earnings growth over the next five-year period alone. Investors looking to add some serious fortification to their portfolio before the next market storm strikes should definitely take a second look at this high-growth stock.