Research from advertising think-tank Credos on behalf of the Advertising Association (AA) also found less than one in four (23%) of the ad sector believes Brexit offers international growth opportunities.
In contrast 39% did not think Brexit would offer the chance of international growth and 28% were unsure of the consequences.
The AA commissioned research on the hopes and concerns of the ad industry ahead of its annual summit, which will have Culture Secretary Karen Bradley as the keynote speaker.
Maxus Worldwide chief executive Lindsay Pattison believes the confusion as to what ‘Brexit means Brexit’ actually means has caused "more caution and focus on prudence and costs".
Pattison remains relatively optimistic Brexit will not have a "massive Impact" in 2017.
Jonathan Trimble, chief executive at 18 Feet & Rising, says it will not be possible to measure the direct impact of Brexit until the UK leaves the EU.
He said: "Circular punditry about High Court rulings and what trade agreements look like is the can of insecurity that’s been poured into the 2017 forecasting.
However, he believes there is also opportunity for business that "prove they can connect with the disenfranchised middle and continue to invest in innovation and marketing".
The headline figures from Credos’ research are part of a wider survey on Brexit’s impact, which will be discussed at the AA’s Lead 2017 conference
Keynote speaker Bradley is expected to outline her department’s needs from industry as Government prepares to negotiate a departure from the EU.
She will speak before BBC Newsnight’s Evan Davis hosts a panel on Brexit, featuring Daily Mail commentator Isabel Oakeshott, Deborah Mattinson of Britain Thinks and Marco Tinelli of FullSIX Group.
Stephen Woodford, chief executive of the AA, said: "Europe is a big part of UK advertising’s global success, so it is incredibly important and positive that Karen has agreed to join us at Lead, and continue our conversation with Government about the risks and opportunities of Brexit."
Bradley was appointed secretary of state in July 2016, after two years as Home Office parliamentary under-secretary.