Manager Jerry Manuel had the entire complement of position players healthy and on the field at the same time Monday for the first time this season. Still, the Mets lost to the Diamondbacks 13-2.
A team source said Monday that left-hander Oliver Perez was in Phoenix, but is not due to be activated until later in the series.
Perez officially is on the disabled list with right knee tendinitis, but the Mets wanted him in the minor leagues anyway.
"Based on the fact that he's had four [minor league] starts and is progressing, we're optimistic that he's going to be ready to join us here shortly," assistant GM John Ricco said.
Regardless, Perez won't re-enter the Mets' rotation when he's ultimately activated as Hisanori Takahashi will make his scheduled start Thursday against the Los Angeles Dodgers.
Manuel said he intends to have Perez work as a lefty-on-lefty specialist in the bullpen -- an expensive one at that, since Perez is only midway through the second season of a three-year, $36 million deal.
A scout who watched Perez's performance Saturday with Triple-A Buffalo indicated Perez's velocity ranged from 85-88 mph and that he gave up "two monster bombs" while walking two in a "liberal strike zone." Officially, Perez was charged with three runs in 6 2/3 innings for the Bisons.
"You probably would like to have seen the velocity and things a little better," Manuel said. "But I still think that as a reliever, he could offer us something -- left-on-left, kind of uncertain where he's going to pitch it. I think that's to his advantage left-on-left."
While Perez could help the bullpen, Castillo's return from bruised feet should stabilize the Mets' lineup. Castillo was in the Mets lineup Monday for the first time in six weeks after the team activated the second baseman from the disabled list.
Castillo, who was batting .241 with 14 RBIs and seven stolen bases this season, batted eighth in the full lineup, which included Reyes leading off and Angel Pagan batting second. On days Jeff Francoeur starts over Pagan in right field, Castillo could move to the No. 2 hole. Castillo went 2-for-4 and scored a run in the loss.
To make room on the roster, the Mets optioned 20-year-old infielder Ruben Tejada to Triple-A Buffalo.
Center fielder Carlos Beltran, who was activated from the disabled list Thursday after missing the season's first half while recovering from arthroscopic surgery on his arthritic right knee, also is scheduled to play. Beltran received Sunday off to allow him to ease back into action after playing three straight games.
Adam Rubin covers the Mets for ESPNNewYork.com. Information from The Associated Press contributed to this report.