"I think that the optimism that we have read about in newspapers in recent days is probably not well founded. Nothing has been agreed yet," Coveney told Ireland’s RTE radio on Friday, Presstv Reported.
"There is very intensive efforts now to try and find the combinations for each other in terms of the two negotiating teams. But as I say we shouldn't draw any conclusions from that. We don't have any agreement yet. And I think we need to be realistic about time frames," he added.
The Irish foreign minister said, however, that he hoped Brexit negotiators would be able to make a "big step forward" ahead of the EU summit in Brussels on October 18.
"The negotiating teams are hard at it this week and will probably be negotiating intensively through the weekend as well and will hopefully have some political recommendations to feed political leaders early next week," he noted.
Coveney's remarks come as UK Finance Secretary Philip Hammond said negotiations with the EU have become more positive, however, insisting that there were still some big differences left to be resolved.
Britain and the EU are locked up in intensive discussions on how they can set out post-Brexit relations as part of an agreement that would also introduce a two-year transition period.
Issues like trade and the future state of the border on the Island of Ireland remain two key stumbling blocks in talks. The two sides hope they could reach a deal in November although there are still chances of a no-deal situation where Britain would crash out of the EU without regulating trade and other issues.
The Irish government wants a written guarantee that there will be no hard border with Northern Ireland, something Dublin emphasizes can only be achieved, in effect, by keeping the region within the single market and customs union.
However, London has repeatedly made clear that Britain will leave the single market and customs union, regardless of the border implications.