Bitcoin fell back below $90,000 on Monday, extending losses after its steepest monthly decline since the 2021 crypto crash, as renewed risk aversion drove investors out of stocks and digital assets.

The world’s largest cryptocurrency fell by as much as 6.1% at one point. By 9:42 GMT, it was down nearly 5% at $86,754, set for its biggest one-day fall in a month and hovering near last month's eight-month low of $80,553.

Bitcoin shed more than $18,000 in November, its largest dollar loss since May 2021, when a number of cryptocurrencies collapsed.

Given its relatively short lifespan, there is not much in the way of seasonality to guide traders' expectations for how bitcoin usually behaves in December.

On average, since its inception in 2012, bitcoin tends to rise by around 9.7% in December, ranking it third in terms of performance, with October being the strongest month, with an average gain of 16.6%, and with September, the weakest month, with an average loss of 3.5%. Of more relevance might be bitcoin's tight correlation with the stock market at the moment, analysts said.

"Bitcoin tends to be a leading indicator for overall risk sentiment right now, and its slide does not bode well for stocks at the start of this month," XTB research director Kathleen Brooks said in a note.

"There is no obvious driver (on Monday), however, the sharp decline in volatility last week, the VIX fell back below the average for the last 12 months, may have unnerved some investors who remain concerned about an uncertain outlook into year-end," she said.

Ether, the second-largest cryptocurrency by market value behind bitcoin, was down 6% at $2,840, having lost some 22% in value in November, the most since February's 32% slide.

Jefferies strategist Mohit Kumar said that a number of crypto-negative factors heading into the weekend were adding to the pressure on bitcoin on Monday.

S&P Global downgraded its rating of Tether, the world's largest stablecoin last week, citing an increase in higher-risk assets in its reserves and "persistent gaps in disclosure," which Tether said it "strongly disagrees" with.

Meanwhile, Phong Le, chief executive of Strategy, the world's largest corporate owner of bitcoin, told the "What Bitcoin Did" podcast on Friday the company would consider selling its holdings if its "mNAV" metric - the company's enterprise value against the value of its bitcoin holdings - fell below 1. That ratio is currently around 1.19, according to Strategy's website.

Shares in Strategy and other crypto companies such as Coinbase and miners Riot Platforms and MARA Holdings were down between 3-4% in premarket trading.

Since hitting a record of around $4.3 trillion in size, the entire crypto market has lost over $1 trillion in value, according to CoinGecko.

U.S.-listed exchange-traded funds backed by spot bitcoin witnessed record outflows of $3.43 billion in November, according to LSEG data. So far this year, a net $21 billion has flowed into these products.