Monell also gives Terry Collins an additional left-handed bat off the bench.
Campbell, 28, was recently relegated back to the bench after having started 15 games at third base in place of the injured David Wright. He hit .286 through his first seven starts, but then slumped batting just .138 his last 38 plate appearances.
Monell, 29, had been batting .397 with a .455 OBP, four HR and 15 RBI in 58 at bats with Triple-A Las Vegas. He agreed to a minor league contract with an invitation to major league spring training this past winter. Monell hasn’t appeared in a big-league game since 2013, when he had one hit and three strikeouts in nine plate appearances with the Giants.
To make room on the 40-man roster, the Mets moved minor league outfielder Cesar Puello to the 60-day disabled list, according to reporter Adam Rubin (May 5).