Mr Prasarn was responding to concerns of possible liquidity shortages because commercial banks are competing for deposits and offering high interest rates.
He said the government had now confirmed that 40% of the 2 trillion baht it intends to borrow for infrastructure megaprojects would be raised overseas, mainly through bond issues, which should ease any problems.
The remaining 60%, or 1.2 trillion baht, would be borrowed from domestic banks, the Finance Ministry has said.
As much as 500 billion to 600 billion baht in excess liquidity is still being absorbed by the central bank each day, Mr Prasarn added.
"The central bank has closely assessed the situation and it is certain that there will be no liquidity shortage," he said.
Responding to concerns by the private sector that economic growth would fall below 4% this year, given analysts' projections, he said the central bank's Monetary Policy Committee would take forecasts into account when it holds its next meeting on Oct 16.
The MPC left the benchmark interest rate at 2.50% at its last meeting in August, saying it was appropriate for the economy to gain momentum. Most economists expect no change at the October meeting.
Mr Prasarn declined to comment on whether he believed gross domestic product growth (GDP) for 2013 would reach 4.2%, as earlier projected by the central bank.
The Fiscal Policy Office (FPO) on Friday reduced its GDP growth projection for the year to 3.7% from 4.5%, mainly because of the slowdown in exports.
The dollar value of Thai exports will increase by only 1.8% this year, instead of 5.5%, said FPO director-general Somchai Sujjapongse.
The office said the government must speed up spending on planned investment projects to spur the economy, particularly in the first three months of the 2014 fiscal year starting on Oct 1.
The FPO projected GDP growth next year would be between 4.6% and 5.6%, with export expansion of between 6.5% and 8.5%, helped by economic recovery in the country’s trade partners.
Inflation is forecast to range between 2.3% and 3.3%, the FPO said.
Continuing sluggishness in manufacturing suggests that the economy may struggle to emerge from recession.
The fifth straight month of contraction in manufacturing output, worse than the market had expected, has fanned debate on when the economy can pull out of a downturn.
Industrial output in August fell 3.12% from a year earlier, led by weakness in cars and electrical appliances. The fall was more than twice the median forecast of a 1.15% decline. Output fell in July by a revised 4.9%.
Capacity utilisation dropped to 63.45% in August from 64.54% in July, according to the Industry Ministry.
The baht completed its worst week this month in response to the reduced economic forecast and concern that the recession will deter foreign inflows.
The currency weakened as the UK bank Barclays cut its 2013 economic expansion forecast for Thailand to 2.5% from 3.5%. It cited a domestic credit crunch, waning stimulus and lack of confidence.
The economy shrank on a quarterly basis in the first two quarters, the definition of a technical recession, while exports fell for three months through July before a slight rebound in August.
The baht dropped 0.6% from a week ago and was trading late Friday in Bangkok at 31.30/35 per dollar, compared with 31.12/19 on Thursday, and 30.94/96 a week earlier.
The baht has fallen 1.4% from a two-month high of 30.88 on Sept 20 touched after the Federal Reserve decision to maintain its record stimulus. The SET Index has declined 4.9% over the same period.
"The economy is likely to remain on the downtrend in the second half due to the slowdown in exports," said Thammarat Kittisiripat, an economist at TMB Bank.
"The baht will depreciate and fund outflows in the short term will continue."