"It is essential for the national credibility when a country signs an agreement and the other party delivers then both parts will deliver on the agreement. Anything else will seriously undermine the national credibility of any country," Stoltenberg told the Kathimerini newspaper in an interview.
He added that he "strongly believes" the agreement would be ratified soon.
"Meaning that this can happen quite early next year," Stoltenberg specified.
The NATO chief also stressed that Macedonia would be able to join NATO only given the deal’s ratification and subsequent changes to its constitution.
The Greek parliament is expected to ratify the deal once Macedonia completes all necessary constitutional amendments on the name change, though rallies opposing the deal have been held in some parts of Greece.
The Macedonian parliament ratified the deal in July, paving the way for the September 30 referendum on the country's NATO and EU membership. The possibility of accession was earlier impossible due to the naming dispute.