As the UK officially notifies the EU of its departure from the bloc, 84% of financial advisors believe the implications of Brexit pose a threat to five-year investment returns, according to research by Prudential.
This is in comparison to 66%, who are concerned about potential market falls, as a result of them being overvalued, with 63% worried about delivering income for their clients.
Low long-term interest rates are also a concern for 55% of advisors, with worries about returns over the next five years leading to seven out of 10 feeling obliged to offer smoothed multi-asset investment solutions.
Prudential investment expert, Vince Smith-Hughes, said: "Brexit is overshadowing all other investment planning issues and highlighting the need for solutions that can provide protection and the possibility of strong returns.
"The triggering of Article 50 will provide some certainty for financial planning but will continue to highlight the need for solutions and advice which can support individuals in achieving their investment goals in the short-to-medium term."
It was found that six out of 10 advisors believe there will be a medium-term market correction, while 76% say smoothing of investment returns is more attractive to clients when market conditions are challenging.
However, worrying about the impact Brexit might have on returns could be the worst thing for investors to do at this time, according Kames Capital CIO, Stephen Jones, who believes exercising undue caution could be a missed opportunity.
He said: "The biggest risk right now is that investors over-worry about disruptive events or financial crises that are unlikely to happen and play it too safe in their asset allocation.
"Strong democracies have developed robust institutions that moderate and implement policies that get through crises, and cash is a wasting asset against a backdrop that is both higher growth and higher inflation.
"You see it again and again in the UK when we get ourselves into the most amazing pickles, but the institutions of government step in and the machine cranks up and gets us through.
"There is pragmatic application of policy. And we shouldn't underestimate that."