Until Sunday night, the impact of COVID-19 on sports in the U.S. felt almost entirely theoretical.

Not anymore.

The BNP Paribas Open, known more commonly as the Indian Wells stop on both the men’s and women’s professional tennis tours, was canceled Sunday due to coronavirus concerns just before it was scheduled to start this week and with many players already in the Palm Springs, California, area preparing for the event.

Though tennis doesn’t always move the needle for mainstream sports fans in America, this is a very, very big deal. Indian Wells is often referred to as tennis' "fifth Grand Slam," a tournament that typically attracts all the top-ranked men’s and women’s players because of the significant prize money and ranking points at stake.

Citing the public health emergency declared by the Riverside County Public Health Department due to a local case of COVID-19 and "the safety of the participants and attendees," tournament organizers went ahead and canceled the tournament, making it the biggest sports event in the world to become a victim of the coronavirus.

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Given the importance of that event on the calendar, the significant amounts of sponsorship money and local tourism dollars at stake, you can be sure that tournament organizers didn’t make that decision lightly.

Now we can only wonder whether it’s the first of many.

Up to this point, there’s been a lot of discussion about whether NBA games or even the upcoming NCAA basketball tournament might be played in empty stadiums while the country tries to contain the spread of COVID-19.

Now it’s totally appropriate to question whether some of these events, at least in the near-term, will happen at all.

Maybe that’s an overreaction. Maybe the tennis tournament could have been played as scheduled without incident, or perhaps they could have played without fans in attendance and not created as big of a stir.

But the fact that such a major sporting event is gone from the calendar in the blink of an eye seems like a potential turning point. In countries like China and Italy, the impact of COVID-19 on everyday life has been so pervasive that sporting events are way down the list of concerns. As the number of cases increases in this country, it’s worth wondering whether the same is going to happen here.

The NCAA tournament, which begins in fewer than two weeks, is going to be played in Sacramento and Tampa, where there have been confirmed cases of COVID-19. It’s also headed for Spokane, which is only a few hours from the epicenter of the outbreak in Seattle.

Over the course of the tournament’s three weeks, the NCAA will be in 13 cities all over the country. Given the rate of new confirmed cases, can anyone be sure it’s safe to hold the tournament in some of those cities?

While the natural impulse for most of us is to continue on with our lives while taking the appropriate precautions, this is clearly an unprecedented situation. It’s really hard to envision a virus altering the major benchmarks of our sports calendar because we’ve never dealt with something like that before. But once a major event like Indian Wells is canceled, it seems more realistic that others will follow.

That’s not a guarantee, of course, and there’s no point in being alarmist. But realistically, if a case of COVID-19 in the general area can derail one of the five or six biggest tennis tournaments in the world this year, it’s worth wondering whether more cancellations are on the way.

Follow columnist Dan Wolken on Twitter @DanWolken.