"When we receive a credible offer that will not leave doubts about achieving a viable solution, we will be the first to take it," the source told reporters.
He underscored that all the draft proposals submitted by the creditors so far have been variations of an offer put forward earlier this month.
"If it does not lead to sustainable debt, it is not worth mentioning. We want a viable solution."
Tsipras said earlier he rejected the creditors' latest ultimatum, which included additional austerity measures, and declared Sunday's referendum to let voters decide whether or not to accept the creditors' offer. Tsipras has put his weight behind a 'No' vote, while the European leaders are urging the Greek public to vote 'Yes.'
The Greek leadership is continuing negotiations with the lenders to resolve its massive debt problem with the Tuesday night deadline, when the current bailout expires, edging ever closer.
