It's been a rough couple of days for freshly public Roku (ROKU -3.31%), maker of its namesake media streaming players. The company has received not one, but two analyst downgrades over the past two days, which has caused shares to plunge after a steep jump in the final months of 2017.

Roku's first public earnings release went rather well, with the company crushing its ongoing transition to the platform business, but the subsequent share-price surge may not have been warranted, and Roku's valuation looks incredibly stretched right now. Here's what investors need to know about the downgrades this week.

The Roku Channel on a TV

Image source: Roku.

A tale of two downgrades

Yesterday, Morgan Stanley analyst Ben Swinburne dropped his rating on Roku shares from equal weight to underweight, according to Tech Trader Daily, while increasing his price target from $25 to $30. Swinburne's biggest concern is the fact that Netflix and Alphabet subsidiary Google's YouTube represent a disproportionate amount of viewership, and Roku essentially does not monetize those channels.

Those companies likely leverage their sheer weight and popularity in order to get favorable terms in negotiating with Roku, and if consumers continue shifting toward those channels, the trend is incrementally negative for Roku's financials. It's rather telling that YouTube is the most viewed ad-supported channel on the platform but Roku receives exactly zero revenue from YouTube, underscoring how strong YouTube's hand really is when negotiating (one of the major risks that I highlighted when Roku first filed its S-1 in September).

"Further, we receive no revenue from YouTube, the most viewed ad-supported channel by hours streamed on our platform for fiscal 2016 and the nine months ended September 30, 2017," Roku wrote in its most recent 10-Q. "If we fail to maintain our relationships with the content publishers that account for a significant amount of the content streamed by our users or if these content publishers face problems in delivering their content across our platform, we may lose users and our business may be harmed."

This morning, Citi analyst Mark May followed up with his own downgrade from neutral to sell, while tweaking his price target from $27 to $28. May is worried that Roku's valuation looks overdone after the recent run-up, with Roku's enterprise value now trading at 8.7 times 2018 estimated revenue. As far as why shares have gained this much, May speculates that a small float and lack of pure-play over-the-top (OTT) alternatives have contributed. Furthermore, there are potential downside catalysts on the horizon, including a lock-up expiration in March, while larger tech giants continue to push deeper into the OTT space.

With shares trading around $47 even after plunging from these downgrades, there's still quite a bit of downside if either of the analysts' price targets prove accurate.