The last-minute absences of scheduled performers and nominees Chris Brown and Rihanna prompted some fast reshuffling at Sunday night's Grammy telecast, including a hastily put together ensemble performance by Justin Timberlake, Boyz II Men, Al Green and Keith Urban.

Brown, who was both a nominee and a scheduled performer, was being investigated for allegedly assaulting an unidentified woman the night before the show. He turned himself in to authorities as the show was being broadcast and was briefly held before posting $50,000 bail Sunday night, jail records showed.

Rihanna's whereabouts weren't immediately known.

"Rihanna is well," her publicist said in an email to the Associated Press that didn't elaborate.

Brown and Rihanna are dating and were both multiple Grammy nominees.

Rihanna was set to be the second performer on Sunday night's CBS show, singing Live Your Life and Disturbia.

Instead, the ensemble performance went on after an awkward, impromptu-sounding introduction by Dwayne (The Rock) Johnson, who had been scheduled to introduce Rihanna.

Brown was scheduled as the evening's fifth performer, singing Forever, but his performance was scratched.

LL Cool J, who had been scheduled to introduce Brown, instead joined Jay Mohr in introducing Sugarland and Adele.

Recording Academy chairman Neil Portnow said he found out three hours before the telecast that Rihanna would not be appearing. 

"There's that minute of anxiety, 'OK, what are we going to do?,' but that passes very quickly," he said backstage after the show.

"We're live television and the Grammys have a history of 50 years of putting on these great performances," Portnow said.

"Things happen, sometimes things change and you have to be nimble and quick on your feet."

Portnow declined to comment on Brown's circumstances, but said he hoped the situation wouldn't overshadow the 51st annual Grammy Awards.

"Musicians are like everyone else, they have their trials and tribulations," he said. "It's not something I want to be judgmental about."