Mr Johnson has said he is targeting the October 17 gathering as an opportunity to strike a last-minute deal.
IRISH PM Leo Varadkar has told Boris Johnson he must table a new backstop plan before the end of next week.
He said Brussels needs detailed written proposals within ten days or “it’s very hard to see how we could agree something” at next month’s crunch EU summit.
He insisted the current deal can’t be “amended or cobbled together late at night” when EU leaders gather for a make-or-break meeting on the 17th.
After holding talks with Donald Tusk, Mr Varadkar said: “It’s essentially the way the EU works.
“If the UK does have meaningful proposals we really need to see them in advance so they can be worked through and worked up in advance of the summit.”
Mr Johnson has said he is targeting the October 17 gathering as an opportunity to strike a last-minute deal.
And the Irish PM’s deadline gives him breathing space to table a full plan with EU negotiators after the Tory party conference, which finishes next Wednesday.
Brussels officials have long suspected Mr Johnson would resist proposing anything in detail before then for fear of alienating the ERG and DUP.
The EU Parliament’s negotiator Guy Verhofstadt revealed Britain’s ideas for an Irish border fix only amount to “partial proposals” so far.
Panning the UK’s technical papers, he said: “They’re only a partial response to a potential alternative, not a fully fledged legally operative alternative.
“In that way it’s not acceptable to say OK, the backstop can fall and we put that partial proposal in place.”
British negotiators tabled a new dossier on Tuesday with plans for the movement of agricultural goods between Great Britain and Northern Ireland.
The paper fleshes out the checks farmers and food producers would face when shipping products into an all-Ireland agri-food zone.
One official described Britain’s proposals so far in the area of customs as “pretty desperate”.
Meanwhile officials in Brussels and national capitals are still pessimistic the PM will be able to come up with a plan they consider to be workable in time.
A senior EU diplomat said: “We still have quite some miles to go. This requires some careful legal work that you can’t write hastily.