For years now, the Call of Duty series has been a constant in the gaming industry. The franchise is the definition of a juggernaut: no matter how many people complain, or trash the game or refuse to buy it, the series continues to sell millions upon millions of copies. Call of Duty games are basically guaranteed to selling tens of millions of copies, regardless of what customers and critics will say.

Though, the franchise's invulnerability may be at an end. According to industry analysts, this year's Call of Duty: Advanced Warfare may not fare as well as its predecessors.

Sterne Agee analyst Arvind Bhatia, while speaking with CinemaBlend, expects the series to see a 15 percent decline in sales with Advanced Warfare. Unfortunately for the series, Advanced Warfare simply doesn't have the same number of pre-orders that Call of Duty: Ghosts had before launch. It's not a sure-fire indication that sales for Advanced Warfare will be bad by any means; it simply hints at a drop of Day One sales.

While 15 percent sounds massive, for Call of Duty, it's not truly on the same scale. The game was originally expected to sell 20 million units, but that number has been pulled back to 17 million. That's a big difference, but a successful release in today's gaming industry is typically anything over one million. Basically, Call of Duty still has a long way to go before the series goes under.

According to Bhatia, there are several reasons for low numbers, many of which have to do with Call of Duty: Ghosts. Released in 2013, Ghosts is considered by many to be the worst Call of Duty game in years, and while the game was still successful, it wasn't on the same level as other games in the series. Word-of-mouth surrounding the game was absolutely terrible, with many arguing that the game hasn't really evolved since 2009's Modern Warfare 2. On top of that, last-generation console sales have been cut in half, and for a cross-generational game like Advanced Warfare, that means more and more people are hesitating to buy the game.

Despite the setbacks, Advanced Warfare could have a chance to recoup those lost numbers. So far, the game is garnering much better word-of-mouth than Ghosts, and it's entirely possible that fans are simply waiting for reviews to be released instead of buying the game on launch day.

There's still a very good chance that Advanced Warfare will sell extremely well, but there's also the possibility that this could be the first sign of over-saturation. The only way to know for sure is to wait for the sales numbers to be released.

Call of Duty: Advanced Warfare will be released on Nov. 4.