James Woolsey, a former CIA director who served as Trump's senior adviser on national security until last month, also believes the G20 would be a good time for the leaders to get together at an early date.
"The key is to not get bogged down in rhetoric, but to start working together on getting things done," he said.
Dr Gal Luft, the co-director of the Washington-based Institute for the Analysis of Global Security, said both leaders should meet as soon as possible "to establish personal bonds and learn to know each other".
"I would argue that the first five minutes of the meeting is the most critical part because we are dealing with two alpha males here. They need to understand each other, but more important, like each other," Luft said.
"Personal chemistry that will emerge, or not, from this will define the relationship and I cannot over emphasise this point. If they like each other, they can do business together and call each other when things are not right. But if the chemistry is not that good, then the relationship will develop in a totally different trajectory," he said.
If Trump chooses to skip the Hamburg G20 summit, the most likely opportunity for a meeting between the two leaders would be the annual Asia-Pacific Economic Cooperation summit in Vietnam later this year.