Saturday's Frankfurter Allgemeine Zeitung newspaper said the continuing economic crisis and chaotic situation in Greece had prompted the sales ban.
The Greek government has paid for imported medicines with bonds due in a few years since the spring. But many firms receiving these sold them at a big loss, the paper said.
Erbitux is approved for use in many countries and carries indications for colorectal and head and neck cancers. It is Darmstadt-based Merck's second most important drug, the paper said.
Merck is not the only company to stop selling pharma products to Greece. Biotest halted sales of a blood plasma product in June due to millions of euros in unpaid invoices.
Merck's Finance Chief Matthias Zachert told the Börsen-Zeitung financial paper that other crisis-ridden countries had made progress. He said the Spanish government has taken action to reduce its debt to pharma firms.