Facebook Inc (NASDAQ:FB) releases its fourth quarter earnings report tomorrow, and shares rose as much as 3% today ahead of those results. Apparently some investors are doing the opposite of what MarketWatch contributor Jeff Reeves recommends. He thinks investors should hurry up and sell before that report comes out.

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Facebook’s future looks dim to some

Reeves notes that Facebook Inc (NASDAQ:FB) had an incredible year of growth last year, but he suggests that this year will be different, even drawing comparisons to Apple Inc. (NASDAQ:AAPL)’s fall from grace starting in late 2012. He notes that Apple’s slide was triggered by disappointing earnings, and he suggests that Facebook will see the same fate this time around.

He sees the biggest risk as being in Facebook Inc (NASDAQ:FB)’s growth story, and he thinks that the social network is experiencing falling new user numbers as the market becomes saturated. He calls our attention to the second and third quarters of last year when Facebook added just one million new users in the U.S. and Canada, marking a growth rate of .5% sequentially.

On a year over year basis, he said the third quarter’s new user number was up 5.3%. In addition, he notes that Facebook Inc (NASDAQ:FB)’s European numbers are “only slightly better.” Reeves thinks that Wednesday’s report will hold the social network’s first sequential decline in North America or Europe, or even both regions. He also notes that data from GlobalWebIndex shows that 83% of Internet users around the globe already use Facebook, which means growth is bound to slow down in the not-too-distant future. He said in order for the social network to keep growing, it will have to hit 90% saturation. Or new Internet users will have to keep popping up around the globe and quickly signing up for Facebook after they’re online.

Facebook’s profits challenged

Reeves also sees potential challenges to Facebook Inc (NASDAQ:FB)’s profits. He notes that as the number of the social network’s monthly users has flattened out, so has the number of users who are on it every day. During the third quarter, Facebook saw a 1.4% sequential growth in the U.S. and 3.2% in Europe. Year over year growth was 9.1% in the U.S. and 17.5% in Europe. The reason these two markets are especially important for Facebook is because nearly half of the social network’s revenue came from the U.S., while more than one-fourth of it came from Europe.

He does note that Facebook Inc (NASDAQ:FB) has continued to grow average revenue per user and that bulls expect this metric to be the main driver of the company’s future growth in earnings. However, he thinks this has limited upside and carries the potential to alienate users at a rate which could offset the larger margins. As a result, he questions whether growth in this area is sustainable, particularly if users stop checking into the social network because they don’t like the extent to which it is monetizing its offerings.

According to Reeves, he isn’t “rooting Facebook to fail,” and he does note that Apple Inc. (NASDAQ:AAPL) managed to make a comeback—although this morning’s selloff doesn’t look promising. However, he thinks that investors who got into Facebook Inc (NASDAQ:FB) early and have enjoyed significant gains should get out—at least partially—while they’re still ahead—just in case.