Talks of a trade war with China have momentarily taken a backseat to increasingly acrimonious negotiations with Canada, Mexico and the European Union, as President Donald Trump spent much of the last week exchanging barbs with major economic partners.

However, one veteran market watcher warned that investors should stay vigilant on the threat from China – because it could roar back to roil markets if the U.S.-North Korea summit goes awry.

"We're relying on China for help there so I don't expect Trump and company to start blasting China with tariffs in anticipation of this meeting," Jack Ablin, chief investment officer at Cresset Wealth Advisors, told CNBC's "Futures Now" on Thursday. "If China is smart what they're going to do is string Trump and Company along with North Korea."

China has positioned itself as an invaluable resource to the U.S. in pressuring North Korea to denuclearize, Ablin said. That has given the country a bargaining chip against any trade threats, and the Trump administration may be loath to antagonize Beijing if the Chinese can help sway Pyongyang.

Trump is set to meet North Korean leader Kim Jong Un face to face in Singapore on Tuesday. The Trump administration has said the aim is full denuclearization, something North Korea is not expected to give up without a fight.

"But, if these negotiations go south or there's some disappointment, I expect these tariffs will be back on the table," Ablin added.

Meanwhile, the chances of a trade conflict with China are far higher than the markets anticipate, says Ablin.

"The likelihood of an outright trade war with China is probably 30 to 40 percent," the investor told CNBC. "So it's not a main, huge risk but I will say if you ask the average investor about the possibility of a trade war with China, they'd probably tell you it's 10 percent."

He added: "I do think I want to err on the side of caution."

Ablin said tariffs on China, the world's second-largest economy, would be "enough to create a sizable [downward] catalyst" for the U.S. stock market.

As for the potential for the North Korea summit itself to be market-moving, Ablin says expectations are so low that any development would be a positive.

"It's really only upside pretty much," he said. "Most observers are not expecting much and so if anything comes of it, it will be positive but that said it will likely just kind of string things along."

Markets have not moved as much on North Korea-U.S. developments recently. When Trump called off the summit on May 24, the ended the day 0.4 percent lower. After the June 1 announcement that it was back on, the S&P gained 1 percent.