The Thai baht has flipped from Asia's strongest currency in 2019 to one of the region's worst performing this year, following an outbreak of a new coronavirus that originated from China.

The Thai currency has lost around 4.1% against the U.S. dollar so far this year, reversing almost half of its 7.9% gains against the greenback in 2019.

In a bid to boost the Thai economy, the country's central bank, the Bank of Thailand, on Wednesday unexpectedly cut its policy rate to an all-time low, and cited the virus spread as one reason that will drag down growth.

Trinh Nguyen, senior economist at French investment bank Natixis, said on Thursday the second-largest economy in Southeast Asia has been too dependent on external demand," particularly that from China.

Nguyen told CNBC's "Squawk Box Asia" that tourism revenue from China accounts for around 2.7% of Thailand's gross domestic product, while exports to China make up some 6% of the country's GDP.

"We know with absolute certainty that the tourism hit will be there," she said, adding that exports are also likely to be "another downward drag" on Thailand's roughly $500 billion economy.

"This is why we slashed GDP forecast to only 2.2% this year and that means that Thailand is very short of the World Bank target of 5% if it wants to reach high income status in about a decade," said Nguyen.