THQ core mouthpiece Danny Bilson's confirmed the new game from Turtle Rock will be formally announced later this year.
Bilson said the title was "the most well-thought out design from the beginning I've ever seen," he told Eurogamer at E3.
"It's an incredible design. I can't wait till we share the concepts of that game, because there is some gameplay in there I've never played before," he said.
"Those guys are really smart. They were the Left 4 Dead team and that was fun. This one's wild. I can't wait to share that one. People are going to go nuts.
"Everybody, when they hear that design, unanimously they just go, wow. I promise you'll do the same when you hear what that game is."