Rihanna had one of the most elaborate 'Saturday Night Live' performances ever, which implies that a whole lot of work went into putting them together. However, sources say that RiRi refused to participate in one of the most integral parts of the effort: her dress rehearsal.

TMZ reports that 'SNL' producers, including head honcho Lorne Michaels, are furious with Rihanna for calling in sick on the all-important dress rehearsal ... because she didn't appear at all sick to anyone. Sources said Rihanna appeared fine and even walked around between songs snacking on an apple (what, no 'Birthday Cake?'). Though no one called her out on her truancy, they were all extremely ticked about it.

The dress rehearsal is live for the studio audience and goes down right before the actual show, letting staffers fix any last minute issues before showtime. TMZ says that Michaels was ticked and shocked that Rihanna canceled at the last minute, forcing her choreographer to fill in. 'SNL' staffers said they can't remember the last time anyone missed a dress rehearsal.

In fairness to RiRi, sources close to the 'Where Have You Been' singer say that she attended every single rehearsal except the dress rehearsal, which she said she was simply too sick for. Rihanna reportedly had her doc administer a penicillin shot right before her performance. Perhaps her illness explains why her vocals left a little bit to be desired. In any case, here's hoping she gets well soon!

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