* Euro stabilizes after Monday's sell-off, remains fragile
* Greek debt concerns underline euro zone problems
* Canadian dollar hits one-week high after inflation data (Adds comment, updates prices)
By Wanfeng Zhou
NEW YORK, April 19 (Reuters) - Solid euro zone economic data helped the euro rebound against the dollar on Tuesday after its worst day in five months but nagging worries about debt troubles in Greece looked set to keep the single currency vulnerable.
The euro climbed above $1.43, well off a two-week low of $1.4155 reached on Monday, when fears mounted that Greece will have to restructure its debt possibly as early as summer. Traders cited technical support near $1.42 and automatic buy orders that were triggered above $1.4250.
The euro zone composite PMI, a measure of the private sector combining services and manufacturing, nudged up to 57.8 from March's 57.6, beating forecasts for a fall to 57.1 and showing business activity in Germany and France continued to outpace the rest of the 17-member common currency bloc.
"Coupled with recent data showing elevated price pressures, robust economic data in core euro zone countries have helped sustain rate hike expectations," said Samarjit Shankar, managing director of global FX strategy at BNY Mellon in Boston. "This has buoyed the single currency despite the lingering sovereign debt crisis in the region's peripheral markets."
The euro was last trading up 0.5 percent at $1.4309, after rising as high as $1.4327 on Reuters data. It fell about 1.4 percent on Monday, the biggest one-day percentage drop since November.
Expectations the European Central Bank will continue raising interest rates to control inflation after hiking this month for the first time since 2008 pushed the euro above $1.45 last week. The currency, however, has come under renewed selling pressure in recent days as worries about debt troubles in peripheral economies resurfaced.
Traders said the euro could encounter more selling ahead of the Easter holidays. Net euro long positions rose to their highest since December 2007 in the week to April 12, positioning data showed on Friday, leaving scope for a reversal.
The Canadian dollar firmed to a one-week high after data showed Canada's annual inflation rate in March jumped to its highest since September 2008, ratcheting up pressure on the Bank of Canada to resume raising interest rates soon.
The U.S. dollar fell as low as C$0.9548 and last traded at C$0.9581, down 0.6 percent on the day.
GREECE RISK
A German government adviser said on Tuesday that a restructuring of Greek debt was inevitable, raising pressure on Athens to seek a solution to the debt woes that are shaking investor confidence in the euro zone. Athens has repeatedly denied such a possibility.
Greece sold more than 1.6 billion euros of three-month debt on Tuesday, with yields rising above 4 percent. Foreign demand also shrank.
Analysts said the possibility that a country which has received a bailout may still have to restructure its debt will likely encourage more investors to exit long euro positions.
"The prospect of debt restructuring continues to weigh heavy on traders' minds given its negative impact on the European financial sector," said Boris Schlossberg, director of currency research at GFT in New York. "The euro could be subject to further volatility if credit conditions in the periphery continue to deteriorate."
The U.S. dollar slipped 0.3 percent to 82.41 yen, while against a basket of currencies, it fell 0.6 percent to 75.050.
Standard & Poor's threatened on Monday to downgrade the United States' prized AAA credit rating unless the Obama administration and Congress find a way to slash the yawning federal budget deficit within two years.
Given that a majority of U.S. debt is owned by foreign investors, some analysts were surprised the S&P announcement of the change to its outlook to negative from stable failed to trigger lasting dollar selling. (Editing by James Dalgleish)