The Mets plan to have a new bullpen option available Saturday.

Jose Castillo, a southpaw who had lackluster performances before being designated for assignment by Arizona, is set to join the Mets prior to their matchup with the Yankees.

The Mets acquired Castillo on Thursday for cash considerations.

Castillo, who is without minor league options, pitched to an 11.37 ERA in five appearances for the Diamondbacks this season.

Team brass on Friday hadn’t ruled out the possibility that Genesis Cabrera would remain on the roster to give the Mets two lefties in the bullpen.

Cabrera has thrived in a hybrid role — short relief and multiple innings.

He entered Friday with a 1.80 ERA in four appearances for the club.

Dedniel Núñez, Huascar Brazobán and Max Kranick all have minor league options remaining.

The Mets have been on the lookout for lefty relief since losing A.J. Minter and Danny Young for the season.

Minter tore a lat that necessitated surgery.

Young has a torn elbow ligament and will undergo surgery.

Frankie Montas was scheduled to throw a live batting practice session in Brooklyn.

According to manager Carlos Mendoza, the right-handed pitcher will participate in at least one more live batting practice in the upcoming days before being considered for a minor league rehab assignment.

Montas opened the season on the injured list after he was diagnosed with a high-grade lat strain early in spring training.

According to Mendoza, Sean Manaea will undergo a “series” of mound throwing sessions to prepare for longer pitching stints designed to mimic multiple inning outings.

The left-hander is rehabbing from an oblique strain that has sidelined him since spring training.

Paul Blackburn was set to start for Double-A Binghamton on Friday in a penultimate rehab outing before he’s considered for a return from the injured list.

The right-hander has been rehabbing from right knee inflammation.