Usher (Michael Loccisano)

The move will give Green and Aguilera a break from the show’s grueling schedule to focus on their “other” careers.

Usher and Shakira will join Adam Levine and Blake Shelton for the show’s 4th edition.

“The Voice” is a bright spot on NBC’s lineup as it struggles to regain ratings — this past Monday’s episode averaged 14 million viewers. The network’s reliance on “The Voice” in the summer, spring and fall, calls to mind ABC of the late ‘90s, when the struggling network hit a ratings jackpot with “Who Wants to Be a Millionaire?” At one point, three nights a week of “Millionaire” were also the country’s three most watched prime-time programs. But through over-use, “Millionaire” began to collapse in 2001 and was dead as a prime-time broadcast series by the summer of ’02 (though a version lives on in daytime syndication).

Though NBC did not launch “The Voice” until the summer of 2011 – buying the Dutch format after losing out to Fox in a bidding war for Simon Cowell’s “The X Factor” -- it is already on its third cycle.

The fall cycle is, arguably, the most important, as it gives NBC a rare ratings magnet off of which to premiere new series as it kicks off a new TV season. Last week, for instance, the time-slot debut of NBC’s new Matthew Perry comedy, “Go On,” launched Tuesday after “The Voice,” averaging nearly 10 million viewers and finishing in the week’s Top 10.


And this past Monday, the unveiling of NBC’s “Revolution” right after another “Voice” auditions episode, logged a healthy 12 million viewers, making it the top premiering drama on any network in three years, and on NBC in five years.

Meanwhile, Fox’s new drama “Mob Doctor” — airing Monday in the teeth of “The Voice” — got gnashed, scoring just 5 million viewers.

In Tuesday’s announcement, NBC insisted that Aguilera and Green will return to the show “next year,” which presumably means next fall.

Aguilera, NBC noted, is releasing a new album and going on tour while Green is “developing new music,” as well as scripted comedy series for the network based on his life.

“Doing two back-to-back cycles on this show requires a tremendous amount of time, and we are happy to accomodate the commitments made by Christina and Cee Lo. The participants on our show benefit from the coaches’ expertise and their continued success in the music business allows for significant new contributions to the contestants when they return,” NBC entertainment chairman Bob Greenblatt said, by way of explaining the exit of two of the show’s stars.

“Since this year NBC and ‘The Voice’ have decided to tape back-to-back seasons, requiring a full-year committment, it is important for me to take season four off, allowing me to support my music my fans have been waiting for — with the release of my new album “Lotus” on November 13,” Aguilera said in the announcement, by way of plugging her new album. “By pursuing my first passion of music during the break, I am also able to come back and offer even more to my team on ‘The Voice’ in the future.”

”Thank you NBC for supporting my decision to take this season four hiatus!” Green added. “It says that I’m seen and respected as a complete artist and not just a cast member.”

But, with three broadcast TV primetime singing competitions cluttering the landscape — “The Voice,” “X Factor,” and Fox’s “American Idol” — these programs have increasingly become about the celebrity judges, with the actual competitors relegated to roles of props and bit players. This week’s “The Voice” announcement comes on the heels of Fox’s confirmation, over the weekend, that Nicki Minaj and Keith Urban have been added to the judges table on “American Idol”when it returns in the first quarter of ‘13.

“The Voice” (Kevin Winter/GETTY IMAGES)