Brexit trade negotiations and Covid-19 are “two perfect storms”, a Welsh Government minister has said.
Lesley Griffiths, who is responsible for rural affairs, said “the window of opportunity to secure a deal is getting very, very small”.
The UK is due to leave the EU without a trade deal unless an agreement can be found before the end of the year.
The UK government says it wants to reach an agreement with the EU during 2020.
On Thursday, business leaders warned that a no-deal Brexit would be catastrophic for British firms.
Dame Carolyn Fairbairn, from industry body, the CBI, told the BBC that any buffers to cope with the additional cost and planning of an exit from the EU customs union and single market without a deal had been exhausted by the Covid-19 pandemic.
Earlier this month a UK cabinet minister said a deal was still possible with the EU, after both sides admitted little progress had been made.
Talks broke up last week, with sticking points including future fishing rights in UK waters and commitments to maintain a “level playing field” over regulation and competition.
Giving evidence to the Welsh Parliament’s Climate Change, Environment and Rural Affairs Committee, Lesley Griffiths said: “It’s two perfect storms I would say, and I think it’s incredibly concerning that the UK Government are remaining adamant that we will be leaving.
“The transition period will end on the 31st of December. Clearly the window of opportunity to secure a deal is getting very, very small.”
“Personally, I don’t think it’s doable. I don’t think the Welsh Government believe it’s doable.”
Representations have been made by the Welsh and the Scottish Governments to extend the transition period, according to Lesley Griffiths.
She said: “We’re now in the middle of June, by the end of July the big trade negotiations should have been closed. The threat of a no-deal Brexit is increasing.”
“It’s the same officials that are dealing with EU transitions and we’ve had to deal with Covid-19. So I don’t think nightmare is too strong a word. It is incredibly difficult to do everything that we need to do but of course we are trying to manage that,” she added.