Moody’s cut its rating on Greek debt four notches to Ba1, a speculative rating that the firm says connotes “questionable” credit quality.

The move comes six weeks after rival Standard & Poor’s spurred a monthlong global flight to safety by cutting its rating on Greek debt to junk.

Moody’s decision won’t immediately hurt Greece, because it hasn’t been borrowing in the market thanks to the bailout plan — though it reportedly has been considering a short-term debt sale next month.

Moody’s cited “considerable uncertainty surrounding the timing and impact” of a giant bailout package announced this spring in a bid to keep Greece from defaulting on its debt.

“Moody’s believes that the Eurozone/IMF support package has sheltered the Greek government from the markets while it enacts the very ambitious fiscal austerity measures and structural economic reforms stipulated by the package,” said Moody’s analyst Sarah Carlson. “These have the potential to restore market confidence, depending on the effectiveness of the government’s execution, and place the country on a more stable debt trajectory.”

But it’s not clear Greece will be able to stage an economic recovery at a time when many of its neighbors are dealing with the same stresses, and even giant economies such as the United States are struggling with mighty debt loads of their own.

Thus the risk of a Greek default, while slim, has risen, Moody’s said.

“The macroeconomic and implementation risks associated with the program are substantial and more consistent with a Ba1 rating,” Carlson said.

Moody’s said Monday that its outlook on Greece is stable, meaning it doesn’t expect to make another change for a year or more.

S&P downgraded Greece to junk six weeks ago, sending investors fleeing from the debt issued by cash-strapped states in the south of Europe. Moody’s said last month it was studying the situation. Fitch, the third big rating agency, downgraded Greece to its lowest investment grade last week.

The cut comes as the euro zone shows strains from the worries about the health of member states and the region’s banks. European lenders could face billions of dollars in losses should a southern European state such as Greece, Spain or Portugal default.

The European Central Bank has tried to ease those strains by sidelining the rating agencies, allowing it to buy government bonds without a high rating. For now, at least, those policies are helping to keep a nervous market stable.