Steelers
Source: Erik Daniel Drost, Wikimedia Commons.

You can add this to the worries over The Walt Disney Co.'s (NYSE:DIS) TV programming and its sports networks' declining subscriber base: With seven years still remaining on ESPN's $15 billion deal to broadcast Monday Night Football, NFL viewership may have plateaued.

A recent Re/Code report noted that overall NFL viewership last year was down about 1.5% from the 205 million viewers who tuned in during 2013. What's more, viewership overall was boosted by Thursday night football, the series of games that had in the past year aired only on the NFL Network but is now available on CBS affiliates.

At ESPN, average viewership of Monday night NFL games was down almost 3%, from 13.7 million viewers a week to 13.3 million. Monday Night Football got off to a particularly slow start last season, with the first three games down 12% over the prior year.

Indeed, Nielsen numbers show the number of sports fans tuning in to MNF has fallen nearly 10% since 2010.

Espn Logo From Thwwaltdisneycompany

Source:The Walt Disney Company.

That could spell trouble for ESPN, which made a big bet on Monday Night Football when it added 10 years to the deal in 2011.

It's other sports, too
Football isn't the only major sport losing viewers. Ratings of the 2015 NBA Finals made for big headlines this summer, as the battle between the Cleveland Cavaliers and the Golden State Warriors drew the most viewers to a basketball championship series since Michael Jordan's heyday, more than a decade before.

What hasn't drawn as much attention is that NBA viewership on the whole has been down significantly, dropping from a game average 2.5 million viewers in the 2011-12 season to just 1.8 million viewers per game last season, according to SportMediaWatch.com. That's a 28% drop in viewership.

There are sports that are gaining popularity, like soccer. But while events such as the women's World Cup drew record-setting viewership numbers that rival the NBA's biggest games, regular-season soccer action doesn't draw the critical mass in the U.S. that football and basketball do.

Coveted ad time
Viewership is important to Disney, because it helps the company negotiate higher rates with cable companies, and factors into the rates it can charge advertisers during live broadcasts. About 32% of ESPN's revenue come from ads, according to Wunderlich Securities research cited by The Atlantic in 2013.

But it's not the only metric that comes into play in advertising. Even with steady or declining viewership, airtime during live broadcasts of major sports remains in high demand. Despite falling viewership, Monday Night Football was still the most-watched cable series on TV for nine straight years. It also tops the charts in a demographic that many advertisers want to reach: adult men under 50.

Pricey rights
ESPN paid big buck for the rights to broadcast Monday night games. Its 10-year deal was a bet that both NFL broadcasting rights would continue escalating, and also that advertisers will continue to pay more for time during the broadcasts. Declining viewership is a concern on that front.

But there's a flipside to that coin.

The most important driver of revenue for Disney is cable subscription fees, which made up about 60% of the network's revenue in 2013.

ESPN's major sports deals put it in a strong bargaining position with cable companies, as contracts come up for renegotiation. ESPN already commands an industry-high $6 monthly per subscriber, and that figure is expected to continue climbing.

Having MNF and other major sports would also stand to make for a stronger ESPN stand-alone offering, something that could be on the way in as few as five years, from what CEO Bob Iger said last month.

Preparing for tougher times ahead?
So far, we haven't seen signs that these big sports contracts are hurting ESPN or its parent corporation. Third-quarter revenue for Disney's cable division was up 5% over a year ago. But income from the division outpaced revenue growth, coming in at 7%.

That's a good sign, especially since that division generates nearly 58% of Disney's income.

The company also plans to cut costs at ESPN by some $350 million over the next two years, which could be a move to brace the network for not only a slowly growing number of cord cutters, but also for a continuing decline in viewership of the major sports

No doubt, the long-term contracts are a potential liability, but we shouldn't lose perspective. These sports remain wildly popular, commanding huge viewership across entire seasons, as opposed to burgeoning sports such as soccer, which can generate huge ratings, but only if the circumstances are right, as they were for this year's women's World Cup final.

Disney should be able to continue to leverage these sports contracts to its favor, but it's also something we need to keep our eyes on in the quarters and years to come.

John-Erik Koslosky has no position in any stocks mentioned. The Motley Fool owns and recommends Walt Disney. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.