According to The Sun, the star will sing for a Russian billionaire and his guests and is using the gig to prepare for her upcoming dates in Brazil.
A source said: "This is the strongest Amy has felt in a very long time.
"She is determined to go down in history as a world-class performer, not someone who ruined a spectacular talent through drugs. The long road back starts in Moscow. This is like a warm-up with a nice financial bonus."
Her spokesman added: "Amy is warming up for her Brazil dates. She's keen to perform in front of a live audience again."
