Grammy Couples on the Rocks?

TMZ has learned that Lance Armstrong canceled his scheduled appearance Wednesday at the 48th annual Grammy Awards. Armstrong was supposed to be a presenter at the show, but sources tell TMZ the award-winning cyclist canceled his appearance after his break-up with Sheryl Crow became public. Crow, who was engaged to Armstrong, has been nominated and is scheduled to attend.

Reps for Armstrong and Crow could not be reached for comment.

Meanwhile, this year's Grammy show may also be the litmus test for other celebrity relationships rumored to be in trouble. Madonna and Bruce Springsteen are both performing on the show -- there's a buzz that both of their marriages may be on the rocks.

Madonna has been married to filmmaker Guy Ritchie since 2000, and Springsteen has been married to singer Patti Scialfa since 1991. No word if Ritchie and Scialfa will attend Grammys.

Madonna's and Springsteen's reps were unavailable for comment.

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