The massive success of Epic Games' Fortnite is having a detrimental effect on publishers of other online games, according to Bloomberg. Take-Two Interactive stock is down 10 percent over the last week, while Activision Blizzard's is down 9 percent. They publish popular multiplayer games Grand Theft Auto Online and Destiny 2, respectively. Meanwhile, Star Wars Battlefront 2 publisher Electronic Arts is faring a little better. It's down only 2.4 percent.

Both Morgan Stanley and KeyBanc Capital Markets reportedly warned earlier this month that Fortnite's growing popularity could hurt other companies.

"Interest around Fortnite accelerated sharply in the past month to the point where we see tactical risk to other publishers with leverage to multiplayer games in Western gaming markets," KeyBanc analyst Evan Wingren said in a March 9th note.

Fortnite currently has more than 45 million players and recently broke its concurrent player record, with more than 3.4 million logging onto the sandbox survival game at the same time. It also recently launched a mobile version on iOS. It's invite-only right now, but that hasn't stopped players from spending more than $1.5 million on in-app purchases in less than a week.

Although publishers are hurting now, Bloomberg said Benchmark analyst Mike Hickey is optimistic. He points out that Fortnite's demographic is younger than GTA Online's, and Take-Two studio Rockstar Games could launch its own online survival game to bring gamers back into the fold. There's no indication Rockstar plans to create such a game, but admit it. You'd play the heck out of a Red Dead Online.