Poor Rihanna, just after she gets stamped with a lawsuit accusing her of thievery in her 'S&M' video (again), her big-name opening act Cee Lo says he's leaving her Loud Tour!

Halfway into the North American leg of the Barbadian hitmaker's trek across the states, the 'Forget You' singer decided he simply had too much on his plate to continue and gave the big 'f you' finger to the Rihanna tour -- amicably, of course. Understandable, given that he's riding high as a judge on the unimaginably successful NBC singing competition, 'The Voice,' right now. Though, since the first season wraps up with a live finale episode on June 29, what will Green be up to for the next few weeks? Writing a book and working on a new Gnarls Barkley album, naturally.

A spokesperson for the big singer tells the New York Times, "He always puts 100 percent into his work and with the requirements and time commitment to ‘The Voice,’ on top of heading back into the recording studio and an upcoming book, he feels that he wouldn’t give his fans the show that they deserve."

Don't fret -- even though the famed Gnarls Barkley artist has pulled out of his touring responsibilities, RiRi isn't totally alone on the road. J. Cole is also out on the Loud Tour, which pulls into its last stop at Boston, Mass.' TD Garden on July 24.

Watch the Cee Lo 'Forget You' Video