Irish premier Micheal Martin has said he is not "overly optimistic" about a breakthrough in the Brexit talks, saying he is "50-50" on a deal being reached.
The Taoiseach described the talks as on a "knife-edge".
Negotiations resumed in Brussels on Sunday after Boris Johnson and European Commission president Ursula von der Leyen gave the green light for talks to resume.
The discussions on reaching a trade deal are entering their final days, with both sides hoping to overcome significant differences on fair competition and fishing rights.
Mr Martin said it is very important that "common sense prevails" and that a post-Brexit trade deal is reached.
"I think the situation is serious and the three issues that prove very difficult to reconcile all the way through the talks are still there to be dealt with," Mr Martin added.
"Namely, the level field, which is proving particularly difficult, fisheries and of course the dispute resolution mechanism to deal with the level playing field issue.
"My sense is that we are at a very difficult juncture and it's important that the Zoom talks use every piece of creativity they can, that the participants try and get a resolution, because a no-deal would be very damaging to all concerned, to the United Kingdom, to the Irish economy and indeed to the economies of member states as well.
"It's very, very important that common sense prevails here and that a deal is done."
He urged Irish businesses to "double down" on their preparations for Brexit.
"In terms of a no-deal it will be significantly more onerous on businesses out there," Mr Martin told RTE.
"Things are on a knife-edge and it is serious."
Mr Martin said it was his gut instinct that it was 50-50 on getting a Brexit deal.
"I don't think one can be overly optimistic about a resolution emerging and my sense, having spoken to some of the key principals here, that this is a very challenging issue to resolve, particularly around the level playing field," Mr Martin added.
"The important dimension here is to get a deal and to make sure it's a deal that works in the medium to longer term because a good sustainable relationship with the UK and EU is what makes sense for the medium term.
"If it takes an extra couple of days to get this resolved, it's better to do that than to rush this.
"There is an EU Council meeting towards the latter part of this week, but there is every chance these talks could play into that."
Earlier on Sunday, Minister for Further and Higher Education Simon Harris said that a post-Brexit trade deal can be done if both sides are willing to reach an agreement on outstanding issues.
The Fine Gael TD said this is a "crucial week" for the EU and the UK to secure a deal.
Mr Harris told RTE's The Week In Politics programme: "It is good to keep talking, it is important to keep talking, but in many ways the difficult issues have been the same difficult issues from the start – it's about fair competition and fisheries.
"It can't be seen about fisheries in isolation, it's about the logical, fair rationale that if Britain wants access to lots of EU markets it's entirely appropriate that EU would have access to British fishing waters while respecting British sovereignty."
Sinn Fein's Eoin O Broin said there are "huge concerns" among Irish exporters over issues around access to EU markets.
Mr O Broin said the deal must be in the interests of the Irish people and businesses, particularly those in the fishing and exporting industries.
"The Government needs to continue what it has been doing which is defending the Good Friday Agreement and defending the Irish protocol," he added.
"We are in the last chance saloon. The costs of this deal are already very substantial and we wouldn't be able to cope with a no-deal scenario."