In a "digital disruption" note, Citi said the rise of fintech companies will mean these traditional banks reduce employee numbers by 30 per cent in the next decade.
Investment in fintech has grown from $1.8bn (£1.25bn) in 2010 to $19bn in 2015, according to Citi.
Kathleen Boyle, managing editor at Citi GPS, wrote in the report that traditional financial institutions “still have the upper hand in terms of scale” and no tipping point has been reached in the US or Europe yet.
But she added: “Given the growth in FinTech investment, this isn't likely to continue for long.”
The Citi report predicts that between 2015 and 2025 there will be another 30 per cent reduction in full-time staff - representing more than 1.8m positions - mainly from retail banking automation.
This would mean the annual rate of decline increasing from two per cent currently to three per cent.
According to Citi, there were 6.19m full-time employees working for traditional banks in the US and Europe at their peak. This figure has now reduced to 5.46m and is predicted to fall to 3.62m in 2025.
The report said banks' "Uber moment will mean a disintermediation of bank branches rather than the banks themselves".
Citi said the Uber moment will lead to a "shift to mobile distribution being the main channel of interaction between customers and the bank".
The report said: "The return of having a physical branch network is diminishing. The concept of retail banking profitability equaling outlet profitability will no longer be valid. Branches will be only one of the distribution channels.
"They will still play an important albeit diminishing role."