Rihanna was "very tired" at her album release party on Tuesday (20 November).
The Diamonds hitmaker had been due to celebrate her latest album Unapologetic at New York nightspot 40/40 following her show in the city - the final date of her 777 tour - but her hectic schedule from playing seven gigs in seven countries in seven days left her in a low-key mood.
Onlookers at the venue said Rihanna arrived shortly before 2am, but took to a private room with family members, which included her brother and cousins, to sip cognac.
One source told the New York Post newspaper: "She seemed very tired."
The 24-year-old pop star also angered reporters who had been waiting for hours by refusing to stop on the red carpet.
However, the You Da One star appeared in more lively form on Thursday night (22 November) after flying to Germany to spend Thanksgiving with her former boyfriend Chris Brown.
Rihanna was seen in the audience of the Yeah 3x hitmaker's gig in Berlin, and the pair later left together for the after-show party at a nearby nightclub.
The Bajan beauty was seen downing shots, while Brown covered his head with a scarf in a bid to stay incognito.