Facebook chief Mark Zuckerberg - AP

Facebook investors are braced for the social network to report a second consecutive decline in European users as it shows more evidence of saturation in its most profitable markets, despite worldwide growth.

Analysts at Deutsche Bank predict the effect of new data protection laws and a September cyber-attack that forced it to log millions of people out of their accounts will hit user numbers in Europe, Facebook’s most lucrative area outside North America.

In July, Facebook revealed the number of Europeans logging in every month had fallen by a million. While a minor decline, it was the first drop in monthly usage in any region. Globally, growth in the last quarter was the slowest ever recorded and the day after the results, $120bn (£94bn) was wiped off Facebook’s market value, the largest one-day loss by a public company in history.

It is yet to recover and this week’s results will be a crucial test of whether July’s drop was a one-off blip or ­evidence of a wider malaise. Deutsche Bank analysts recently downgraded forecasts for this week’s results, saying they were “unlikely to be a positive catalyst” for the company’s share price.

The social-media giant’s problems have continued, including a recent cyber-attack in which hackers stole the details of 40m customers.

In late September, Facebook logged 90m users out of their accounts in ­order to protect them from the attack. This may affect the company’s daily user numbers – a key indicator of how loyal users are.

The social network is also expected to give a first estimate of how much it expects to spend next year. Investments in thousands of moderators as well as in server and telecoms equipment have limited profit growth, ­although the company is expected to report quarterly profits of $5.2bn, up 11pc on last year.

It comes after social media rivals Snapchat and Twitter both revealed declines in user numbers last week.

Facebook shares are currently ­trading at their lowest price in more than a year amid a broad sell-off in technology shares.