The song, called 'Gimme Pressure', is the latest number to appear online from the former Sugababe's highly anticipated debut LP.
Lyrics to the track, penned by the star, include: "I heard the rumours from London to California/ You're taking shots at my name/ I'll put it on ya/ I'm a veteran, got the upper hand/ Ten years on the top".
The line suggests a reference to Buchanan's time in the band, after spending ten years in the group before being ousted moments before shooting a music video in the Vasquez Rocks of California.
The leak marks the third song to appear on the web from Buchanan's solo recording sessions, after 'Fearless' surfaced online last year and 'Under Control' leaked last month.
Buchanan recently told