If global growth doesn't pick up, the bull market will face a major hurdle, market watcher Scott Wren says.
Wren, senior global equity strategist at the Wells Fargo Investment Institute, ranks it as his top risk — ahead of a potential Federal Reserve policy mistake and ongoing trade tensions.
"I think really an all-out trade war is a relatively low probability. I'm more worried about: Is global growth going to slow down, stabilize, what's going to happen there?" he said Wednesday on CNBC's "Trading Nation."
It's largely an effect of central banks around the world simultaneously ending easy money policies. Wren sees the actions possibly bleeding into the U.S. stock market because so many American companies rely on business all over the world.
"We need some help from the overseas economies to get to the earnings estimates, and the type of targets that we're looking at," he said.
Wren doesn't see much upside left this year in the stock market. He predicts the could end the year as much as 4 percent lower than current levels, citing a fair value-type scenario.
"Valuations are not cheap. They are not extremely stretched to the upside, but I sense we could be in the early innings, very early innings, of the chasing activity that would typically take you to the top," Wren said. "That could play out over a year or two."