The euro zone was most likely in recession in the third quarter, a private sector survey showed Wednesday, a day before the European Central Bank’s governing council meets to discuss monetary policy.


Business activity and new orders in the 17-nation currency bloc declined in the three months through the end of September, according to a survey of purchasing managers by Markit Economics, a financial data provider. Markit said its composite index came in at 46.1 in September, ticking down from 46.3 in March but revised up from its initial estimate of 45.9.


A value below 50.0, where the composite index has remained for eight straight months, suggests the economy is contracting. Ireland was the only country to report an increase. German activity was largely unchanged, and French activity fell sharply.


Chris Williamson, Markit’s chief economist, said in a statement that it appeared “inevitable” that the euro zone returned to recession in the third quarter, following a 0.2 percent decline in the second quarter. The commonly accepted definition of recession is two consecutive quarterly declines in gross domestic product.


“There therefore seems little scope for a return to growth in the fourth quarter,” Mr. Williamson said. “The uncertainty is perhaps whether policy makers will be able to induce an improvement in business and consumer confidence to help ease the rate of decline, or whether the pace of downturn will accelerate further towards the end of the year.”


The E.C.B. meeting Thursday comes as Spain, which is battling to meet demands for fiscal consolidation amid a devastating recession, is thought to be preparing to ask its European partners for a bailout. Prime Minister Mariano Rajoy said Wednesday that no bailout request was imminent.


After a period of intense activity to calm the euro zone crisis, the E.C.B. is not expected to announce major new policy actions Thursday following a meeting of its governing council in the Slovenian capital of Ljubljana.


Last month, Mario Draghi, the president of the E.C.B., set out the terms for the central bank to begin buying bonds of countries like Spain to hold down their borrowing costs. One of the conditions was that countries must request help from the euro zone bailout fund. Until Spain takes that step, the E.C.B. is not likely to buy Spanish bonds.


The E.C.B. is not expected to cut the benchmark interest rate, which is already at a record low of 0.75 percent. Mr. Draghi has expressed concern that the official rate is no longer having much effect on borrowing costs for business and consumers in the troubled countries.


The rationale for E.C.B. bond buying is that by lowering the cost of government borrowing, interest rates in the private sector would also fall. Market interest rates in euro zone countries like Italy tend to track the rates that their governments pay.


In addition, a rate cut now would leave the E.C.B. with few policy options if the situation in the euro zone deteriorates further.


“While a rate cut could easily be justified by the economic outlook,” analysts at ING wrote in a note Wednesday, “we think that the E.C.B. is not yet willing to fire this very last shot.”


European stocks were mixed in afternoon trading Wednesday. The Euro Stoxx 50, a barometer of euro zone blue chips, was down 0.13 percent, and the FTSE 100-share index in London was up 0.11 percent.


The Bank of England is also due to announce an interest rate decision Thursday, though most observers believe the central bank will not enact any new stimulus measures in light of recent data showing that the British economy is strengthening.


The euro was at $1.2903, down from $1.2940 late Tuesday in New York.


David Jolly contributed reporting from Paris.