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We're told it's looking very good that Nicki and Britney will reach an agreement in the next day or so.
Nikki would take the place of Enrique Iglesias -- who bailed at the last minute because his ego could not take opening for Britney.
Nicki is currently on tour with Lil Wayne -- those concerts end on April 28. Britney's tour begins June 17 in Sacramento.
Source: TMZ