Papadopoulos, a former foreign policy adviser to President Donald Trump's 2016 campaign, pleaded guilty in October to lying to the FBI about meetings with individuals closely associated with the Russian government during the campaign.
Mueller said in a court filing with a federal judge on Friday that Papadopoulos' "crime was serious and caused damage to the government's investigation into Russian interference in the 2016 presidential election."
His filing did not specify a particular sentence for Papadopoulos, but noted that under legal guidelines his sentence could range from no time in prison to up to six months.
Mueller's sentencing memo also noted that although Papadopoulos "agreed to meet with the government to answer questions" before he pleaded guilty, he did not offer "substantial assistance" to the Russia investigation.
Papadopoulos is scheduled to be sentenced on Sept. 7.