Madonna's long-time collaborator Patrick Leonard has posted several demos from the Like A Prayer album online, in an attempt to thwart an auction of the star's personal effects.
Leonard uploaded the first versions of Like A Prayer and Cherish, recorded on the day they were written, on Monday.
He hopes to stop fans bidding on cassettes of Madonna's unreleased recordings at an auction this week.
The tapes are being sold by the star's former art adviser Darlene Lutz.
Lutz is also auctioning intimate personal items including Madonna's break-up letter from rapper Tupac Shakur, a hairbrush with strands of her hair and "stage-worn" La Perla bra.
The singer tried to stop the auction, filing an emergency court order in 2017, saying she had no idea Lutz was in possession of the items. However, a Manhattan judge ruled earlier this month that the sale could go ahead.
The auction is due to end on 26 July. Current bids on Madonna's unreleased music have reached $1,283 (£1,031) for the Like A Prayer demos, $446 (£358) for an original recording of Justify My Love and $963 (£774) for a cassette with an early configuration of the setlist for the star's 1990 Blond Ambition tour.
Although Madonna couldn't stop the auction, Leonard has taken matters into his own hands.
"I hope these posts stop the sale of that cassette at auction," he wrote on YouTube. "Not cool at all that someone would sell it. Not theirs to sell."
The Like A Prayer demo was recorded on "the day it was written," he added. It lacks the finished version's gospel choir and electric guitars, but the lyrics and melody are identical. Madonna also provides some celestial background vocals that were eventually erased from the track.
Cherish retains its breezy pop shuffle, even without the harmonica solo and a capella breakdown that elevate the released version into a pop classic.
Leonard also shared an unreleased song, Angels With Dirty Faces, a lightweight, mid-tempo song which has more in common with Madonna's water-treading Who's That Girl soundtrack than the confessional pop of Like A Prayer.
The title was taken from a 1938 James Cagney Movie - much like the previous Madonna song White Heat. Leonard previously described the track as one "Madonna and I wrote for the [Like a Prayer] album and ultimately must have decided that wasn't good enough".
Earlier this month, Leonard also shared images of a 10-track demo cassette from the Like A Prayer sessions, which is presumably the source of the latest release.
It included working versions of Dear Jessie and Promise To Try (then called Little Girl), alongside Like A Prayer, Cherish and others.
"They're first day versions, so the day we wrote them," Leonard said of the songs. "They have a lead vocal and some backgrounds. Not produced. Without live players and strings and choirs etc. We worked from these versions and they became the records."
The cassette also included the unreleased instrumentals Bossa Nova and 20s Jazz, which Leonard described as "sparks that made no fire".