The singer's 12th studio album headed the US Billboard 200 last week with first week sales of 359,000, keeping efforts from Lionel Richie and Adele off the top.
However, Forbes has now reported that second week sales of the record have slumped by 88%, with MDNA shifting 46,000 copies over the past seven days.
In comparison, Richie's Tuskegee - which landed at number two last week - has experienced a sales slide of 47% and managed to sell 110,000 copies during its second week.
Forbes writer Roger Friedman suggested that Madonna's first week sales number was high due to the star giving away the album free with concert ticket purchases for her upcoming world tour.
He criticised Billboard and SoundScan for counting the promotional copies of MDNA, which were technically not purchased within a traditional transaction.
Madonna celebrated the first week success of MDNA last week by throwing some cake in her manager's face.
> Madonna invites Justin Bieber on tour via 'MDNA' Twitter chat
Watch the music video for Madonna's Girl Gone Wild below: