In 10 games (one start) with the Mets, Verrett is 1-0 with one save and a 1.93 ERA. He pitched eight innings of one-run ball in his lone start against the Colorado Rockies on Aug. 23.
Monell, who hit .178 with four RBIs in 24 major-league games this year, batted .324 with seven home runs and 51 RBIs in 71 games with Las Vegas this season.
Herrera, 21, hit .195 with two home runs and four RBIs in the majors before he was optioned to the minors in late June. He went .331 with 11 home runs and 50 RBIs in 80 Triple-A games this year.