The nine-year veteran began the season with the San Francisco Giants after signing a two-year deal in the offseason. In 59 games, he posted a 68 wRC+ and a -0.8 fWAR while hitting .242 with a .604 OPS. He primarily served as a center fielder, but also appeared in left field as a member of the Giants.
Jackson was traded to the Texas Rangers on July 8 and designated for assignment three days later. He was subsequently released by the Rangers without appearing in a game. The 31-year-old has played for six different teams since being drafted in the eighth round of the 2005 MLB Draft by the New York Yankees. He has a career .274 batting average and .734 OPS.
The Mets have not officially announced a corresponding move, but Matt Ehalt reported on Twitter that Matt den Dekker will be sent down. In 21 plate appearances this season, den Dekker has not recorded a hit.
Joel Sherman added that the signing was not made as a result of an imminent Jose Bautista trade. Bautista, who has been a performed well since signing with New York, has garnered some interest as the deadline approaches and could be moved before Tuesday.