Britain has yet to give legal notice to the EU to quit under Article 50 of the 2009 Lisbon Treaty.
Once it does, it has up to two years to negotiation an exit deal, which will effectively involve its own trade deal with the EU.
Mr McClay said he expected to meet with many European counterparts at the meeting in Shanghai on July 9 and 10.
EU Trade Commissioner Cecilia Malmstrom and UK Minister of State for Trade and Investment will be among the attendees.
Mr McClay is in regular contain with Ms Malmstrom because New Zealand in the midst of preparations to launch FTA negotiations with the EU.
He did not believe that progress on a EU-NZ free trade agreement - a possible conclusion in 2019 - would be significantly affected.
"While it is still very early days in the joint scoping exercise, we are working towards a possible launch of negotiations during 2017 with a potential two-year negotiation," he told the Herald.
He said New Zealand had a significant number of supporters in the EU and re retained a strong relationship with the UK.
"The work we have done over the past few years will be important as we, over the coming months, discuss as orderly way forward for our trading relationship."
Mr McClay said he had already begun talks with New Zealand exporters and would continue to engage with the sectors most affected including the meat, dairy and horticulture industries.
"It is important that they are fully informed and fully engaged in the process as it develops."