Yields on the Greek government’s brand new bonds are already trading at distressed debt levels — suggesting that despite February’s bailout package investors still see a strong chance that Greece will not be able to sustain even its much-reduced debt burden.

As the first week of trading closed, yields on the benchmark 10-years were at 18.24 percent — down from Tuesday’s closing high, but still the highest in the euro zone.

The new bonds have replaced old Greek paper, under a massive €206 billion ($273.5 billion) exchange program that swapped old bonds for new ones carrying lower coupons.

The high yields — the most elevated by far in the euro zone — reflect skepticism about whether the latest rescue deal, based on an orderly default of Greek debt, is enough to prevent a second default in the future. Last month private sector creditors reluctantly agreed to an effective default of 75 percent of the value of their debt, in a deal masterminded by euro zone finance ministers.

Assessing Greece’s ability to meet its fiscal challenge, Mike Turner, head of global strategy and asset allocation at Aberdeen Asset Management in Edinburgh, said, “The aim of reducing the country’s debt-to-GDP ratio from 160 percent to 120 percent by 2020” — the timetable envisioned by euro zone ministers when they put together the second bailout package — “still looks an impossible task without further write-offs.”

The heart of Greece’s problem is that it needs first to halt a rapid decline in its gross domestic product — which could amount to 8 percent this year. Having achieved this Herculean task, it must then start growing its economy again.

An expanding economy would boost tax receipts, allowing it to pay down debt.

But achieving this is an extremely tall order for several reasons, say analysts.

The cuts in spending made to close Greece’s fiscal deficit have already meant redundancies for thousands of government workers, which has cut household consumption. As a result, Greece is in its fifth year of economic contraction — one of the longest recessions suffered by a country in modern global history. This has hit tax revenues — forcing even more cuts in spending that create a vicious cycle.

A second problem is that even in normal times, Greece lacks the ability to generate fast economic growth for a sustained period.