The challenger bank secured a £925 million rescue package over the weekend to shore up its finances.
But customers had already been withdrawing their money from the bank in the days prior, Metro Bank confirmed.
It still expects deposit balances to grow in the next two years, "notwithstanding the recent increase in deposit outflow rates in advance of the announcement of the Capital Package", it said in a statement last night.
Metro Bank share prices plummeted last week after it emerged it needed a cash injection.
Concern for the bank was so high the Bank of England asked larger banks whether they wanted to buy Metro, the BBC reports.
However, it has secured £325m in new funding and refinanced £600m of debt.
Its biggest shareholder is now Colombian billionaire Jaime Gilinski Bacal, who invested £102m via his Spaldy Investments company, to increase his stake to 53%.
Metro Bank still 'very expensive'
More trouble could lay ahead for Metro Bank according to Simon Samuels, former managing director at Barclays and Citi, who told the BBC the lender still had to address the "fundamental challenges" of its operating model. He said maintaining so many high street branches was a "very expensive" strategy.
Metro burst onto the scene in 2010 becoming the first new bank to open a branch in the UK in more than 100 years. It promised to be a 'challenger' bank to the main high street names, saying it would keep branches open seven days a week, with longer operating hours.
It has fee-free accounts and offers perks such as free wifi and refreshments in-branch, as well as instant debit card printing so new customers can start using its services straight away.
But while it now has 2.7 million customers and £15bn in deposits, its 76 UK branches are expensive to run - a reason why many established banks are closing sites across the UK.
Mr Samuels said: "Essentially, Metro finds itself with an unsustainable cost base."
He believes Metro's bricks and mortar strategy has "little chance" of success in the long term, and thinks it could end up being bought out by a larger group.
Metro Bank mortgage
Following the rescue package announcement, Metro said it will cut costs by £30m a year from 2025.
It will also sell off about £3bn in residential mortgages - about 40% of its total.
This has not yet been secured so there is no change to mortgage holders at the moment. If Metro does sell off its mortgages, some customers might see their loans managed by another lender in future.
However, regulations mean mortgage conditions, such as the interest rate and loan duration, would remain the same.
Metro Bank - is my money safe?
Metro Bank said customers' money is safe and the financial rescue package has been "welcomed" by the Prudential Regulation Authority.
For those still worried, the Metro Bank is regulated by the UK and customers are protected by the Financial Services Compensation Scheme (FSCS).
This means if a bank goes under, you'll be able to get your money back up to £85,000. This limit is set per person, not per account.
Mortgages, insurance and investments are also covered.
Chief executive Daniel Frumkin said: "Today's announcement marks a new chapter for Metro Bank, facilitating the delivery of continued profitable growth over the coming years."
Mr Gilinski Bacal said: "I have been an active investor in Metro Bank since 2019. The opportunity to become the bank's major shareholder is driven by my belief in the need for physical and digital banking underpinned by a focus on exceptional customer service."
The Prudential Regulation Authority, which had reportedly been looking for a buyer for Metro Bank, said: "The Prudential Regulation Authority welcomes the steps taken by Metro Bank to strengthen its capital position."