Pedro Solbes has been the EU's commissioner for monetary affairs since 1999, following the sacking of the previous European Commission in a corruption scandal.
He may now become the first top-level casualty of a new corruption scandal surrounding the statistical agency, Eurostat, which formally comes under his command.
No-one accuses Mr Solbes, a former Spanish economy minister, of wrongdoing himself.
Solbes oversaw the introduction of euro notes and coins
But many members of the European Parliament want him to take political responsibility for what went on in Eurostat.
"I accept responsibility for everything I have done and for what I should have done, but not for something I did not know about," Mr Solbes told the parliament's budgetary control committee in July.
But MEPs responded that in many EU member states, government ministers would resign for much less - whether they knew or not.
'Good for Europe'
For the last four years Pedro Solbes has been the European Commission's Mr Euro.
He oversaw the successful and highly complex introduction of euro notes and coins at the beginning of last year, and consistently talked up the currency - arguing that markets were undervaluing it - during its long period in the doldrums.
1942: Born in Pinoso, Alicante province
Education: Diploma in economics, degree in law, doctorate in political science
1968: Starts civil service career in foreign trade ministry
1980s: Helps negotiate Spain's 1986 entry into the EU
1991-93: Minister of agriculture
1993-96: Minister of economy
1996-99: Member of Spanish parliament
1999-2003: EU Monetary Affairs commissioner
While others - such as Central Bank chief Wim Duisenberg and German Chancellor Gerhard Schroeder - occasionally made gaffes that sent the currency tumbling, Mr Solbes stuck to the same message: the euro is good for Europe, the European economy is fundamentally in good shape, and ongoing structural reforms will make it even better.
The soft-spoken 61-year-old, sometimes nicknamed the Whisperer, has also consistently stuck up for the EU's Stability and Growth pact, which limits public deficits in the eurozone to 3% of GDP.
Here too, he has not had an easy time.
Not only have the eurozone's two biggest economies, Germany and France, broken the pact's rules, and argued for more flexibility. Fellow commissioners have also undermined his position.
Mr Prodi last year famously described the pact as "stupid" while trade commissioner Pascal Lamy - rumoured as a possible replacement for Mr Solbes as monetary affairs commissioner - described it as "crude".
Attack and defence
At home in Spain, he has the support both of his fellow Socialists and the conservative Popular Party. There is speculation that his dogged defence of the growth and stability pact is one reason why some people are now out to get him over the Eurostat affair.
Mr Prodi told the European parliament in September that there was no reason for any member of his commission to resign.
But critics allege the European Commission had plenty of warning about the problems at Eurostat long ago - but waited until May before suspending any Eurostat officials, and until July before setting up a commission of inquiry.
However, Mr Solbes' supporters say it was not easy for him to take action while the EU's anti-fraud office was investigating the case. They blame the delay on EU procedures.
External affairs commissioner Chris Patten has also argued that the alleged fraudulent practices at Eurostat date back to the period before the current commission took office, so none of the present commissioners can reasonably be held responsible.