Image source: Flickr user Erin Costa.

The number of people that tuned into Twitter's (TWTR) first Thursday Night Football livestream didn't have a big impact on CBS (PARA 9.71%). Its 243,000 average viewers paled in comparison to the 15.4 million viewers that watched the first week's game on CBS and NFL Network.

At Goldman Sach's Communacopia conference earlier this month, CBS CEO Les Moonves laughed off the threat of Twitter to its business. "Glad to have them showing our games over the [internet]," Mr. Moonves jokingly told the audience. But from there, he went on to discuss one of the biggest ways the NFL is undermining one of CBS's biggest assets.

The RedZone Channel

The NFL launched NFL RedZone in 2009, offering subscribers the chance to never miss a big play. It uses the coverage produced by CBS and Fox to provide a commercial free day full of coverage of everything going on in the NFL. It's a fantasy football obsessive's dream come true.

Importantly, as Mr. Moonves points out, since the channel doesn't show commercials CBS and Fox don't make any money off of it even though they pay for the content rights and production.

The RedZone channel was previously only available to subscribers willing to upgrade their pay-TV bundle to larger, more expensive packages. But it's becoming easier and easier for consumers to receive the channel, specifically with new virtual pay-TV providers like Dish's (DISH) Sling TV and Sony's PlayStation Vue.

A $35 per month RedZone bundle

Sling TV offers subscribers of its $25 per month Sling Blue bundle access to NFL RedZone and several other sports networks for just $10 extra per month. What's more, customers can cancel that added bundle after the NFL season is over. PlayStation Vue is offering NFL Network and NFL RedZone for $39.99 per season (about $10 per month) to subscribers of its $35 and $45 per month plans.

Sling TV doesn't offer CBS, and PlayStation Vue only carries it in select markets. Subscribers looking for a football fix will have to do without or get an antenna.

Importantly, it's unlikely most virtual pay-TV services coming out will carry CBS's broadcast channel. Negotiating local rights with affiliates has been a sticking point for many would-be services, and it's wholly unnecessary considering consumers can receive the channels free over the air. With services coming from Hulu, YouTube, and potentially more tech companies, CBS could find itself losing viewers.

That's especially true considering its own over-the-top package, CBS All Access, still doesn't have access to the Sunday NFL games on CBS's television network. Mr. Moonves is optimistic he'll get a deal done with the NFL. "Eventually that will happen. Sooner than later is my guess."

Just how important is the NFL to CBS?

The NFL rights CBS holds are extremely important for CBS to increase its retransmission fees -- what other companies pay CBS for content. Every time CBS has a carriage fee dispute, CBS can lean on its NFL rights in order to get a deal done. In both its standoff with Time Warner and Dish, Mr. Moonves points out the negotiations ended the night before an NFL game. But if more viewers are watching the NFL on another channel, the NFL doesn't have as strong of a leg to stand on.

What's more, the average Sunday afternoon football game on CBS brings in over 19 million viewers. As such, CBS is able to command huge prices for its ads during the games. What's more, it's able to use the games to promote its shows during primetime, which has enabled it to maintain high ratings throughout the week.

The NFL is a cornerstone to CBS's success, and the ease of access to the RedZone channel and the rise of virtual skinny TV bundles is a real threat to its value.