Stocks across Europe are expected to fall at the open after German Chancellor Angela Merkel and French President Nicolas Sarkozy warned the Greek Prime Minister that he would not receive another cent in aid until his country committed to remaining within the euro.
At a meeting in Cannes on the eve of the G20 heads of state summit Angela Merkel told reporters: "We would rather achieve a stabilization of the euro with Greece than without Greece, but this goal of stabilizing the euro is more important."
IMF managing director Christine Lagarde added to the pressure on Greece saying: "As soon as the referendum is completed, and all uncertainty removed, I will make a recommendation to the IMF executive board regarding the sixth tranche of our loan to support Greece's economic program".
The head of sovereign ratings at S&P believes Greece's decision to hold a referendum will complicate its debt restructuring but will not ultimately change the fact that it will be considered a default.
This referendum "greatly complicated by the internal political dynamics in Greece," said David Beers said in an interview with Dow Jones News wires.
"It may affect the timing and nature of any restructuring" but "it doesn't change, in our opinion, the fundamental fact that Greece is very close to some type of restructuring that will likely amount to a default."
As the pressure mounts on Greece, non-European members of the G20 are expected to push Angela Merkel and Nicolas Sarkozy to get the euro zone's house in order amid reports euro zone leaders attending the meeting will hold an emergency summit behind closed doors in Cannes.
Expect comments refusing to commit to buying bonds from the European Financial Stability Fund as China and other emerging nations use similar tactics to those being used to force Greece's had to apply pressure on Angela Merkel and Nicolas Sarkozy.
If Greece, which will be represented by finance minister Evangelos Venizelos at the G20, takes the prize as least popular attendee in Cannes, Italy's Silvio Berlusconi will come a close second.
With calls growing for him to step down in Italy, the Italian prime minister will arrive in Cannes having failed to win agreement on measures aimed at boosting growth as demanded by euro zone leaders.
Berlusconi's cabinet late Wednesday approved a plan to sell state property, slash red tape and roll out infrastructure projects, according to Reuters news agency, but the plan did not include plans to cut taxes or reform its labor market.
Away from Cannes, the new boss of the ECB makes his debut in Frankfurt.
Like the G20 meeting, the ECB decision on rates and Mario Draghi's first press conference as head of the central bank will be dominated by the Greek issue.
Analysts do not expect a cut in rates on Thursday but on Wednesday Ireland's finance minister said he expects Draghi to cut rates by between 25 and 50 basis points at the December meeting.
Any comments on bond buying by Draghi will be closely watched by the market.