The comments from Philipp Roesler came amid pressure on Greece as the so-called "troika" of international debt inspectors prepares to determine whether Athens has implemented enough reforms and budget cuts to merit more help.
Roesler, who is also the economy minister, leads the pro-market Free Democratic Party — the junior partner in Chancellor Angela Merkel's governing coalition. It often talks tough on Europe's debt crisis.
"Of course we will all wait for the troika report in the autumn, but I will say here that I am more than skeptical," Roesler told ARD television, adding that experts believe "Greece probably will not be able to fulfil its conditions."
"If Greece does not fulfil its conditions, then there can be no further payments to Greece," he added.
Greece has received two bailouts totalling €240 billion ($292 billoin) from other eurozone governments and the International Monetary Fund after bond investors would no longer lend it money at affordable rates. In return for the money, Greece is supposed to cut its budget deficit and reform its economy.
However, the economy has continued to struggle and the new government of Prime Minister Antonis Samaras has said it wants more time to meet some of the conditions. There's little enthusiasm among creditors such as Germany for granting that wish.
A cutoff of bailout money could lead to Greece defaulting on its remaining obligations and possibly leaving the euro.
Asked about the consequences, Roesler said it would first of all mean Greece becoming insolvent — "but then perhaps the discussion will start in Greece itself and the Greeks will themselves come to the conclusion that it is perhaps smarter to leave the eurozone."
"I think that for many experts, for the FDP, for me too, a Greek exit from the eurozone has long since lost its horror," he said. Roesler added that he didn't expect any other countries would leave the 17-nation currency.