Trump, who is due to arrive in London on Dec. 2, is likely to be asked about his attitude to future trade talks.
However, Johnson said he would walk out of trade negotiations if including the health service was a pre-condition.
“First of all the NHS is not for sale. Under no circumstances will this government or any Conservative government do anything to put the NHS up for negotiation in trade talks or privatizing anything like that,” he said. “I can tell you were the United States, or any other country, to insist on that as condition of talks we would simply walk out.”