Right now there are only rumors, but when Dennis Lin tweets a roster move out, it's a reliable statement:
No further concrete information is available at this time. The return appears to be a Player To Be Named Later.
Nick Vincent was out of options in a crowded bullpen, so this move makes some sense. With Matt Thornton being assured of a spot on the 25-man roster and joining certain teammates Fernando Rodney, Carlos Villanueva, and Brandon Maurer, Vincent was competing with a host of candidates including Drew Pomeranz, Kevin Quackenbush, Brandon Morrow, Ryan Buchter, Buddy Baumann, new acquisition Dan Straily, and Rule 5 players Luis Perdomo and Josh Martin for the remaining spots.
The 29-year-old righty reliever is a four-year veteran with the Padres, who drafted him in the 18th round of the 2008 draft. A native of Ramona, the local was a mainstay in the Padres bullpen alongside Kevin Quackenbush and Dale Thayer in recent years.
I'll update this post as I learn more.