[UPDATE] Activision has updated the Modern Warfare Remastered FAQ to more clearly explain that you will indeed need to have Call of Duty: Infinite Warfare's physical disc inserted to play Modern Warfare Remastered. This only applies to people who buy Infinite Warfare on a physical disc.

Here is the new language, as written by Activision:

PlayStation 4

Call of Duty: Modern Warfare Remastered is a full game digital download that will be included in the Infinite Warfare Legacy Edition and Legacy Pro Edition on PlayStation 4. The digital download is redeemed via a voucher code on an insert in the box. The Infinite Warfare game disc must be inserted to play Modern Warfare Remastered. Internet connection is required.

Xbox One

Call of Duty: Modern Warfare Remastered is included on the Infinite Warfare Xbox One disc (no voucher code required) in the Legacy Edition and Legacy Pro Edition of Infinite Warfare. Before Modern Warfare Remastered can be played, an additional download is required. The game disc must be inserted to play Modern Warfare Remastered. Internet connection is required.

Steam

A Steam key will be provided in the Legacy Edition of Infinite Warfare that will provide access to both Infinite Warfare and Modern Warfare Remastered. Internet connection is required.

The original story is below.

What could be a key detail about how you'll be able to play Call of Duty 4: Modern Warfare's remastered version has come to light.

As Call of Duty fansite Charlie Intel spotted, Modern Warfare Remastered's website has been updated with a line of text that suggests you may need the Call of Duty Infinite Warfare disc inserted to play the game. As announced previously, Modern Warfare Remastered is a digital-only game that is available only through Infinite Warfare's premium editions, which start at $80.

Here is the line of text in question: "Modern Warfare Remastered is a full game download (game disc must be inserted to play Modern Warfare Remastered). Internet connection required."

Activision also directs people to this FAQ page, but it doesn't have more details about the "game disc must be inserted" part.

If you're buying Infinite Warfare digitally, this does not apply to you since you won't have a disc, Charlie Intel reported.

One reason why Activision may require you to insert the Infinite Warfare disc to play Modern Warfare Remastered is that it would eliminate the ability for people to sell their copy of the game and continue to be able to play Modern Warfare Remastered.

Activision has not said if Modern Warfare Remastered will ever be sold on its own, though it also hasn't ruled it out. GameSpot has followed up with Activision in an attempt to get more details.

Activision's Raven Software is working on Modern Warfare Remastered, while Infinity Ward, another Activision-owned studio, is building Infinite Warfare. The game arrives on November 4 for PlayStation 4, Xbox One, and PC. You can play Modern Warfare Remastered's campaign on PS4 30 days early if you preorder one of the game's premium versions.

A new trailer for Modern Warfare Remastered was released this week--and it looked great.

This story has been updated and corrected.