"Today is Good Friday for Orthodox Christians, which is day of sorrow when Christ was crucified on the Cross, and Maria has to co-suffer with Christ today and the days ahead," said Potapov, who has visited Butina many times during her imprisonment.
Butina was sentenced at the US District Court for the District of Columbia earlier on Friday. She has been imprisoned since last July and will therefore have to serve another nine months in prison to complete her 18-month sentence.
Before the sentence was handed down, Butina tearfully begged the court for mercy, saying she never intended to break any US laws. But District Judge Tanya Chutkan insisted that Butina's offense was serious and her actions had threatened US national security.
Potapov expressed hope that Butina's faith would see her through the dark days ahead, noting that even on the mournful occasion of Good Friday, Christians look forward to the impending resurrection of Christ.
"This is joyful time, and I hope Maria will experience joy as well, despite the fact she is in prison," he said.
The priest said he would try to visit Butina as soon as possible, hopefully by next week, because "she needs moral support" now.
Potapov sounded a note of regret as he recalled how Butina tried her best to build bridges between Russia and the United States.
"She was probably naive in thinking she could do that during this Russia-gate hysteria," he said.
Butina pleaded guilty to a single count of conspiring to act as a foreign agent as part of a plea deal and had requested a sentence of time served.
Russia has insisted that Butina is innocent, saying she was forced to plead guilty under duress.
Prior to signing her plea deal, Butina was kept in a single cell for 67 days and was not allowed to make phone calls or have any contact with the outside world, the Russian Embassy in Washington has said.
In November, the embassy complained that Butina's solitary confinement exceeded the limits recommended by the Nelson Mandela Rules for the treatment of prisoners.
Russian President Vladimir Putin has said Butina’s indictment was unjustified because she was not charged with working on a mission for the Russian government.