New data from Enterprise Ireland client companies shows one in three have seen their exports decline so far this year.
Some 57% expect the outlook to improve in 2021 and to increase jobs, but 85% expect Brexit to add up to 10% to their cost base.
However some sectors, such as lifesciences and digital, saw export sales grow by 30%.
And more than eight in 10 exporting companies are either confident or very confident about the international trading environment next year.
The survey coincides with International Markets Week, Ireland's largest exporter event.
It will see more than 700 companies meeting 140 market advisors from 40 countries in 2,000 individual virtual one-on-one meetings to plan their COVID-19, Brexit and market diversification strategies.
Travel and other restrictions in many markets present challenges to exporters to find new customers and to stay in touch with existing clients.
Enterprise Ireland CEO Julie Sinnamon told Newstalk Breakfast firms are adapting to the virtual world.
"I think the important thing is that companies continue to engage with their clients.
"It obviously is not optimum, but at the same time we've done a lot of work with companies in the last year on virtual masterclasses, how to conduct business online, how to have technical sales etc, how to build relationships.
"And it is the way that companies have had to go".
"It's a very important week, probably more important than any International Markets Week because of COVID and Brexit both coming together."
She said sectors like construction, digital technologies, electronics and food saw large growth in 2019.
While there was 15% growth in the Eurozone market, UK growth stood at 2%.
She added: "We're seeing pretty strong growth in a lot of regions, and all sectors grew".
Speaking at the official launch of International Markets Week, Tánaiste Leo Varadkar said: "Now more than ever, it is important to assist Irish companies increase their presence in existing markets and expand into new ones.
"The exporting sector will continue to be a strong engine for growth and jobs in the Irish economy as we re-build after the pandemic.
"I'm heartened to see that over half of companies expect to grow their exports next year and that 83% expect to hire new staff.
"This is a testament to the resilience and adaptability of Irish business owners."