The X Factor judge co-wrote 'Scream & Shout' - originally titled 'I Don't Give a F**k' - with Jean Baptiste, according to The Sun.
The song was intended for her debut album The Female Boss, before Baptiste's collaborator will.i.am removed elements written by Tulisa and re-recorded it with Spears.
A source said: "The song was due to be Tulisa's third single from her album until Will told his protégé Jean that he wanted the beat for him and Britney.
"Tulisa's team thought it was a surefire hit but, after losing the battle for the rights, they were forced to release 'Sight of You' which only got to number 18.
"She now has to watch on as the song goes top five around the world.
"At one point Tulisa was even considering releasing her version to rival 'Scream & Shout', but now it's unlikely to see the light of day unless it gets leaked."
will.i.am and Britney Spears's version of the song is on course to reach the top five in the UK singles chart this afternoon (December 16).
Tulisa recently described 2012 as the "worst" year of her life.