Trump vowed last week to remain a "steadfast partner" of Saudi Arabia and said it was not clear whether Saudi Crown Prince Mohammed bin Salman knew about the plan to kill Khashoggi last month at the Saudi consulate in Istanbul.
He then headed to Bahrain over the weekend and traveled to Egypt on Monday where he held talks with President Abdul Fattah al-Sisi.
According to the source, the Moroccan king decided his country was not ready to host the crown prince "at such a critical juncture", the report said.
"It causes our standing in the world to plummet, it telegraphs to despots around the world that they can murder people with impunity, and that this President will have their back as long as they praise him", he said.
While Saudi Arabia has blamed the October 2 killing of Khashoggi on a rogue hit squad, weeks of shifting explanations aroused suspicions.
The New York-based rights group said it had filed a submission with Argentine prosecutors calling on them to invoke the country's universal jurisdiction statute to prosecute the crown prince for alleged war crimes committed by the Saudi-led coalition in Yemen.
Despite the global outrage sparked by Khashoggi's killing, the crown prince has been emboldened in recent days by Trump's vocal support for him.
The crown prince faced an early rebuke during his stopover in Tunisia, where hundreds of protesters gathered late Monday to protest his visit.
London has not taken any action against Saudi Arabia yet but said it is ready to impose sanctions if evidence points to Riyadh's direct involvement.
In Europe there have been calls to end arms sales to Saudi Arabia, and Canada could still be smarting from a diplomatic row sparked by Saudi anger at its criticism over human rights in the kingdom.
In an interview with Sputnik, Saudi energy expert Said al-Shahrani said that "the decision to build a nuclear power plant in the kingdom is the result of serious research that confirmed the need for this step". Trump announced last week that the USA would continue to back the kingdom, despite reported Central Intelligence Agency conclusions linking the crown prince to Khashoggi's demise.