The G20 summit is due to begin in Buenos Aires on Friday and tensions have already started to flare.
Leaders from the world's biggest economies will converge on the Argentinian capital, with a number of high-stakes meetings planned.
But one of the biggest meetings will not happen.
On Friday, Donald Trump called off his meeting with Vladimir Putin over Russia's treatment of Ukraine.
Russia opened fire on the Ukrainian boats and then seized them and their crew on Sunday near Crimea, which Russia annexed from Ukraine in 2014.
Moscow and Kiev have tried to pin the blame on each other for the incident.
"Based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting in Argentina with President Vladimir Putin," Mr Trump wrote on Twitter.
Perhaps the most-watched meeting will be between Mr Trump and his Chinese counterpart Xi Jinping.
Xi Jinping and Donald Trump are due to meet at this week's G20 summit to discuss trade. Source: AAP
Mr Trump has slapped huge tariffs on China, which has responded with tariffs of its own.
White House economic adviser Larry Kudlow said Wednesday Mr Trump is open to reaching a deal on US-China trade irritants but is ready to hike tariffs on Chinese imports if there is no breakthrough.
Mr Kudlow said Trump had told advisers that "in his view, there is a good possibility that a deal can be made, and that he is open to that."
Trump snub?
And while Mr Trump will also meet the leaders of Turkey, South Korea, Germany, Argentina, Japan, India, he won't be meeting Prime Minister Scott Morrison.
A White House schedule for the G20 summit reveals Mr Morrison will miss out on his first formal one-on-one meeting with Mr Trump.
However, a spokesman for Mr Morrison told AAP the prime minister would still have an opportunity to touch base with Mr Trump.
"But given we have no pressing bilateral issues at the moment, and the PM had an extensive opportunity with VP Pence at APEC, there is no pressing need for a formal bilateral at this stage," the spokesman said.
Prime Minister Scott Morrison is off to the G20. Source: AAP
"The relationship is being well-managed."
The opportunity could be in the form of a "pull aside" between the two leaders - an informal discussion on the sidelines of one of the summit sessions.
Frydenberg staying home
Meanwhile, Treasurer Josh Frydenberg has withdrawn from attending the G20 summit alongside Mr Morrison.
He will instead stay in Canberra where the government is dealing with the fallout from losing its majority in parliament.
Finance Minister Mathias Cormann will instead attend the summit, as he has done on three previous occasions.
Quizzed in parliament on Wednesday why he was not attending, Mr Frydenberg said: "It's a leaders meeting."
"The prime minister will represent this country at the G20 meeting, accompanied by the finance minister and he will be talking Australia up, unlike the Labor party which talks Australia down."
Shadow treasurer Chris Bowen said it was another missed opportunity to further Australia's economic interests.
Treasurer Josh Frydenberg won't be joining Prime Minister Scott Morrison at the G20 summit. Source: AAP
"More involvement in the G20, not less, is vital to further Australia's economic interests and cooperation with the world's largest economies," he told AAP.
Former foreign minister Julie Bishop said G20 summits were "hectic".
"But there are many opportunities for world leaders to meet, and the Australia-US relationship is strong and deep and it will continue whomever is in the White House, whomever is in The Lodge," she told reporters in Canberra.
