Olivier Blanchard’s warning follows yesterday's IMF downgrade of its forecast for the UK growth to just 1% for this year.
"We think this would be a good time to take stock," Blanchard said, speaking to Radio 4's Today programme, adding that the global economy was "not out of the woods yet".
Three months ago the IMF prediction for 2013 was 1.1%. The official government forecast for growth is 1.2%.
An IMF report in October warned that austerity had hurt wealthy countries such as the UK more than most analysts had expected.
"We've never been passionate about austerity,” Blanchard told the BBC today. “From the beginning we have always emphasised that fiscal consolidation should be slow and steady.
"We said that if things look bad at the beginning of 2013 – which they do – then there should be a reassessment of fiscal policy. We still believe that. You have a budget coming in March and we think that would be a good time to take stock and make some adjustments."