A U.K. vote to leave the European Union on June 23 would cause major currency fluctuations and dent growth in the country, according to Ramin Nakisa, global macro strategist at UBS.

He estimated it would have an approximately "2 percent impact on GDP (gross domestic product) in the U.K. over the long term." However, the "biggest effect would be on FX (foreign exchange), so we're saying euro/sterling would go to parity if there was an exit," he told CNBC Friday.