Among those who said they were considering quitting Britain were 50% of EU workers with PhDs, 39% with postgraduate degrees and 52% of those on higher incomes who were interviewed for the survey for KPMG UK.
The survey of 2,000 EU citizens found that 45% plan to stay in the UK after Brexit, 35% are considering leaving and 8% have made up their minds to go.
If all of those considering departure actually left, it would reduce the UK’s national workforce by 3.1% - almost one million people - said the consultancy firm.
Some 51% said they would like to hear a clear commitment from their employers that they want them to stay.
KPMG’s head of Brexit, Karen Briggs, said: “Our survey highlights how important the actions of employers are going to be if the UK is to avoid a Brexit brain-drain.
“Although almost half of the EU citizens working in the UK plan to stay, what other EU citizens choose to do is definitely hanging in the balance.
“Against this backdrop we expect to see increased competition for talent between employers over the coming years, and numerous firms seeking to supplement their workforce with AI (artificial intelligence), robotics and automation.”
Half (50%) of those surveyed said they felt less welcomed and valued in the UK since the Brexit vote and 53% said that the Government’s offer to protect their rights after Brexit had made no difference to their thinking.
In a separate poll of 1,000 EU citizens from countries supplying large numbers of workers to the UK, some 49% said that the desirability of Britain as a place to live and work had fallen due to the referendum result.
:: OnePoll questioned 2,000 EU workers in the UK between July 14 and 31, and 1,000 EU citizens living in Poland, Ireland, Romania, Portugal, Italy, Lithuania, France, Germany, Spain and Latvia between July 14 and 25.