A downturn in US home sales and prices is likely just beginning, a prominent economist warned on Thursday.

Ian Shepherdson, the chief economist at Pantheon Macroeconomics, said in a note to clients that the housing market’s recent slump is “still nowhere near the bottom, especially for prices.”

His forecast came after existing home sales dropped 5.9% to a seasonally adjusted annual rate of 4.81 million units in July, according to the National Association of Realtors.