The EU Commission has published its first post-Brexit assessment 19 July

Says the report:

"The economic landscape has not changed much in the weeks since the spring forecast was published on May 3, but the results of the UK referendum on 23 June have modified the conditions for the way ahead. The 'leave' vote has resulted in financial market volatility, abrupt exchange rate changes, and a substantial increase in uncertainty. These developments and the uncertainty resulting from what is expected to be a protracted period of exit negotiations have the potential to damage the recovery in the EU. While uncertainty is expected to diminish over time, forthcoming changes in the economic and political relationships between the UK and Member States could have a longer lasting impact on the medium to long-term economic outlook.

At the current juncture, the economic outlook is mainly affected by the uncertainty resulting from the UK's vote to leave the EU. Without information about the situation after the UK's exit (e.g. trade patterns, mobility of goods, services and labour, policy responses), the 'new equilibrium' is difficult to pencil in and thus the adjustment path is impossible to specify. This implies that the uncertainty shock could evolve quite differently in terms of dimension and duration. The first assessment starts by looking at developments between the spring forecast and the UK referendum. Then, to get an idea about the near-term impact of referendum-related uncertainty, model-based scenario analyses and expert judgment are taken into account to evaluate a 'mild' and a more 'severe' uncertainty shock.

Increased uncertainty has resulted in a deterioration of the growth outlook for the UK but also for the rest of the EU in 2016 and 2017. In recent months the EU economy has broadly developed in line with the spring forecast, i.e. the economic expansion has been sustained at a moderate pace, almost entirely driven by domestic GDP components. Private consumption has benefitted from low oil prices, very accommodative monetary policies and ongoing job creation; investment has accelerated slightly; and net trade has remained a drag on growth. Before the UK referendum, GDP growth in the euro area would have been expected to reach 1.7% in both 2016 and 2017. However, the UK's 'leave' vote is expected to slow private consumption and investment and impact on foreign trade.

Full assessment here