Rihanna's relationship with Shia Leboeff may be in trouble, Mediatakeout reports.

The RnB beauty slipped away with Justin Timberlake after exchanging sexy stares

According toa source, who is a well known actor, Rihanna snuck out of the Palms hotel after-party with Justin and the two weren't seen again for the rest of the night. The insider told MediaTakeOut.com, "Justin and Rihanna were hanging out and [talking] for a while. Then they both got up all nonchalant and left together ... It was crazy because Jessica [Biel] was there and she was looking all over for [Justin] ... Poor girl."

The insider added, "By the way Justin and [Rihanna] were looking at each other, you know exactly what they were going off to do."