After extended Spring Training, Pena, 27, will report to Triple-A Buffalo, the report said.
The right-handed-hitting Pena hit .205 in 64 games for the Nationals last season. For his career, Pena has a .253 batting average with 77 home runs and 225 RBIs in 560 games with the Reds, Red Sox and Nationals starting in 2002.
Last month, Pena refused a Minor League assignment from Washington and was granted his unconditional release. He originally signed with the Mets as an amateur free agent in 1998.
Jesse Sanchez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.