The president said May ignored his advice for Brexit negotiations and instead "probably went the opposite way."
Last week, May reached a deal with her ministers that sets the stage for future negotiations with the European Union. The so-called Chequers agreement calls for the U.K. to maintain a trading relationship with the EU that mirrors its existing relationship as much as possible.
"Well if they do a deal like that it will most likely- because we'll be dealing with the European Union, instead of dealing with the U.K. So it will probably kill the deal. If they do that, their trade deal with the U.S. will probably not be made," Trump told the Sun.
The president went a step further and said former foreign secretary Boris Johnson would "make a great prime minister," although Trump said he wasn't "pitting one against another." Johnson stepped down from the role in protest to the government's decision to maintain its close relationship with the EU.