Legendary investor Jeremy Grantham says the US Federal Reserve is killing the recovery of the world's biggest economy and the ''next bust will be unlike any other''.

Mr Grantham – the cofounder and chief investment strategist at the $US112 billion ($123 billion) Boston-based fund manager GMO –said he wouldn't invest his clients' money in US stocks for at least the next seven years because of the Fed's ''misguided policies''.

High profile investor Jeremy Grantham says the next bust suffered by the world economy is going to be 'very painful'.

Mr Grantham has an impeccable track record, having called both the internet bubble and then the US housing bubble. In November he said he believed the US sharemarket could rise another 30 per cent, although he believed it was overvalued, before crashing again.

''We invest our clients' money based on our seven-year prediction,'' Mr Grantham told Fortune.