Although many investors have felt optimistic about the future prospects of the Canadian cannabis space since the country moved to legalize recreational marijuana use last month, rising stock prices are far from a sure thing. Earlier this week, a prominent short seller revealed that he is making bets again the industry. On Wednesday, Andrew Left, author and editor of investment publication Citron Research, thinks Canadian Cannabis companies are destined to fall in the near future, he said on CNBC's Halftime Report.

Left Is Short Canopy, Cronos and others

According to CNBC, Left explained to Halftime Report host Scott Wapner that he is short such big names in the Canadian cannabis space such as Canopy Growth Corp. (CGC), Cronos Group (CRON) and Tilray Inc (TLRY). Left had previously disclosed his bet against Tilray.

The analyst and short seller predicted declining prices on stocks across the industry, not just for any particular company. He explained: "I'm also short Cronos, I'm short Canopy, I'm short Tilray. So I'm short a basket of names," adding that "once the U.S. licensed producers come on—the faster it becomes legal in the U.S., the quicker the Canada names go lower."

Left suggested that at least part of the reason for his bets against Canadian companies is that "they won't get the exposure in the U.S., they're not players internationally." He quipped that, regardless of "how many press releases they put out, they're not going to be shipping cannabis from Canada to Australia. Not happening."

Shares in all three of the companies indicated above fell to coincide not only with Left's comments but also with the release of Canopy Growth's earnings results.

What it means for investors

Investors keen to get involved in Canada's legal cannabis space may take Left's commentary to heart. There are reasons to believe that Canadian cannabis company's may have limited reach in a global market. Canaccord Genuity analyst Matt Bottomley, who maintains a buy rating on Canopy shares, per CNBC, admitted as much: he blamed poor revenue on "a hiccup in getting products to Germany," among other issues. Whether such concerns are here to stay or not as Canopy develops its international reach remains to be seen, however.

On the other hand, investors may not necessarily agree with Left's assessment. Left suggests that the legalization of marijuana across the United States could doom Canadian companies. However, as of this time, there has been no significant progress toward marijuana legalization in the U.S. at the federal level, although more and more individual states have moved to legalize cannabis in one form or another.

Going forward, investors interested in legal cannabis stockswill have to decide if they believe the hype or if they side with short sellers like Left.