"We started from a deficit of around 15.5 percent. The 2010 deficit we will find out from the statistics authority, I cannot give an estimate but it will very likely be higher than 9.5 percent," George Papaconstantinou told private Real FM radio, according to a transcript posted on the station's website.
Greek reports this week said the slippage was owing to additional pension fund deficits found by auditors from the European Union's statistics service Eurostat who have been in Athens since last week.
If those findings are confirmed, the 2010 deficit could exceed 10 percent of Gross Domestic Product, the reports said, despite draconian spending cutbacks that sparked waves of general strikes and protests last year.
The finance ministry last week said net ordinary budget revenues were down 9.1 percent in January-February compared to last year, and some 860 million euros short of target.
Greece's parlous finances are under scrutiny from the European Union and the International Monetary Fund as Athens tries to put its house in order and meet an EU deficit target of 3.0 percent of GDP.
Athens last year agreed to overhaul its economy and rein in a public debt of over 300 billion euros ($423 billion) in return for a 110-billion-euro EU-IMF loan that saved the country from default.
The Greek Socialist government recently pledged to privatise state assets worth 50 billion euros by 2015 to reduce part of the debt.
Papaconstantinou on Wednesday said the country could pay down some of the debt provided enough money is raised from state asset sales in a programme to be detailed in mid-April.
"If we have enough money from the privatisation programme we could buy back a certain part (of the debt) but we must not think that this will be a cure for all ills."
Athens insists that its draconian austerity measures are producing results but markets remain unconvinced.
Greek long-term borrowing rates remain prohibitively high and the country's credit standing has been hit by successive downgrades from rating agencies, the latest on Tuesday from Standard & Poor's.
The downgrades have further undermined Greece's efforts to return to borrowing from the money markets as proof of returning confidence in its economy.
The government until now has said it planned to issue bonds sometime in 2011. This week, the finance ministry indicated this could happen in 2012.
The EU-IMF recovery programme "anticipates Greece accessing private capital markets by 2012," the ministry said on Tuesday.