Lord Digby Jones has condemned Jeremy Corbyn for his plans to take part in an anti-Trump protest today.
The cross-bench peer said it was "absolutely disgusting" for the Labour leader to publicly oppose the US president, and that it would hinder him if he ever became Prime Minister.
"If Jeremy Corbyn wants to be the Prime Minister of this great nation he is going to have to do wonderful things with America," Lord Jones told talkRADIO's Julia Hartley-Brewer.
"It is our biggest trading partner, biggest inward investor, the guarantor of our security."
The Labour leader is set to speak at the central London protest today, before joining in with protesters.
Mr Corbyn said the protest will be "an opportunity to stand in solidarity with those he's [Trump] attacked in America, around the world and in our own country".
But Lord Jones, who is the former director general of the CBI, urged the politician to "get real".
"He is in a position of responsibility, representing the nation," he added. "Anybody who wants to ban Trump coming or stop him speaking, just get real. This country is so vital to Britain."
"I don't want to see the bloke who wants our vote as Prime Minister sitting down in protest against the guy. That's never going to help him do those deals."
He continued: "I think that it is absolutely disgusting if he wants to do the job, and that is different to exercising your right in our nation to peaceful protest."