What's happening: Shares of TubeMogul Inc (NASDAQ:TUBE) were down 13% as of 11:30 a.m. Monday after BMO Capital analyst Daniel Salmon downgraded the stock to "market perform" from "outperform." Salmon also lowered his per-share price target on TubeMogul shares to $15 from $22. 

Why it's happening: The call arrived ahead of TubeMogul's second-quarter results, which are slated for release later today. Salmon elaborated that while TubeMogul is likely to beat analysts' estimates, BMO is "cautious due to changes in the competitive environment."

While investors will probably focus more on Google's recent decision to remove inventory from the DoubleClick Ad Exchange, Salmon is primarily concerned about the entrance of privately held Appnexus -- which he noted is "likely the largest independent ad tech platform in terms of total dollar flow through the platform" -- into the video buying market. More specifically, Salmon says industry contacts have offered positive feedback on Appnexus' platform, and its "deep embedding at the agency holding companies ... gives it the opportunity to quickly 'turn on' video revenues through this installed base."

That doesn't mean TubeMogul can't continue to thrive. But considering the company still isn't profitable as it focuses primarily on top-line growth in the burgeoning video advertising market, it's unsurprising BMO might choose to remain cautious in these early stages.

For perspective, analysts expect TubeMogul to announce 36.4% growth in second-quarter revenue to $39.2 million, and a quarterly loss of $0.17 per share. TubeMogul, for its part, offered guidance three months ago for second-quarter revenue of $38 million to $40 million, and an adjusted EBITDA loss in the range of $3 million to $1 million.