Sebastian Gorka, who worked in the White House until August, told BBC Scotland Mr Trump “believes that nation states prosper when they are sovereign”.
The US president previously said Scottish independence would be “terrible” because the country could lose the right to host the British Open golf tournament.
Asked whether Mr Trump might favour the break-up of the United Kingdom, Mr Gorka said: “If it makes sense. You’ve got to look at the nickel and dime at the end of the day.
“You’ve got to look at ‘does it economically make sense?’ ‘Is there a future that is connected to devolution’?
“He’s a pragmatist. So if it makes sense, pragmatically, why wouldn’t he support it? I’m not saying he’s there. But he is somebody who looks at the reality not the utopia.”
Mr Trump has often expressed his love of the country, which is the birthplace of his mother Mary Anne Macleod, who was from Lewis.
Mr Gorka is a British-born US military and intelligence analyst, who was a deputy assistant to the president for eight months, from January.
He was interviewed for the Donald Trump: Scotland’s President documentary, which will be broadcast on BBC One Scotland at 9pm on Thursday.