A growing threat of a U.S. trade war with China has only exacerbated existing problems for Apple, according one of the company's biggest critics on Wall Street.

"When you focus in on Apple in particular, the concern is that if we have a trade war with China, that Apple is going to suffer — and it will suffer more so than the other multinational tech companies," Colin Gillis, senior technology analyst and director of research at BGC Financial, told CNBC's "Power Lunch" on Monday.