The move is seen as a fresh start for the 23-year-old Mattingly, who was given a $1 million signing bonus after the Dodgers drafted him as a supplemental first-round pick in 2006 (31st overall) but has struggled on the field in five seasons without advancing beyond Class A.
Hampered by hamstring problems, the right-handed Mattingly batted .194 at Inland Empire and .237 in the Arizona Rookie League, having been moved to the outfield after spending his first four seasons in the infield. His career batting average is .232.
"I'm happy for him and really thankful to the organization," Don Mattingly said. "He had kind of fallen off in playing time and to do this for him at this time was a gift for him."
Pena was a ninth-round pick by Cleveland in 2006 who also hasn't advanced beyond Class A. He hit .148 this year in only 24 games and has a career batting average of .244.