Newell made the comments in a lecture given to the University of Texas' LBJ School of Public Affairs, as reported by Polygon.
"The biggest challenge, I don't think is from the consoles. I think the biggest challenge is that Apple moves on the living room before the PC industry sort of gets its act together," he said.
"The threat right now is that Apple has gained a huge amount of market share, and has a relatively obvious pathway towards entering the living room with their platform. I think that there's a scenario where we see sort of a dumbed down living room platform emerging - I think Apple rolls the console guys really easily."
To avoid this grimly-painted future of unintelligent AppleBoxes, Newell says Valve has to "make enough progress in the PC space to establish" itself, and "figure out better ways of addressing mobile before Apple takes over the living room".
Newell expects a larger number of hardware companies to make their own own bids to establish living room boxes within a year.
"There are going to be a huge set of products that say, 'If you want something that's incredibly cheap, at a price point well below anything that consoles will be able to reach, you're going to take advantage of the PC that's running somewhere in your house," he said.
"It's like one of those things where afterwards it will seem like it was very simple, when beforehand, everyone sort of denied that it was possible."
The Valve co-founder said his company is "happy" to be the one to lead this charge because competitors will be quick to follow, offering consumers plenty of options.
"But they'll have those characteristics. They'll say, 'Well, I could buy a console, which assumes I'll re-buy all my content, have a completely different video system, and, oh, I have a completely different group of friends, apparently,'" he said.
"'Or I can just extend everything I love about the PC and the internet into the living room.'"