An appearance U.S. pop star Britney Spears was to tape for Madonna's upcoming concert tour was delayed due to technical difficulties.

(does that mean she has porked out - or shaved her head again)

Spears was to begin shooting a video montage at a sound stage in Hollywood, however, production insiders told E! Online the shooting schedule had to be pushed back a day because the set was not finished in time.

(hmm, they had to make the doors wider)

"The video will be very deep," a source close to Spears told E! News. "You've never seen Britney like this before. It will blow your mind."

(we've seen britney in every way)

The insider added that Madonna personally invited Spears to be part of the project.

Madonna's publicist, Liz Rosenberg, confirmed to E! Online, "There is footage being shot of Britney some time this week in conjunction with Madonna's upcoming tour."

(maybe they are going to tag team A-Rod)

Stating only that the segment was not a music video, Rosenberg added: "That is all the information I have available. The rest is a secret."

(yeah - secret like the no panties photos)