NEW YORK — A smiling Sean Manaea clutched a ball in his left hand as he strolled around the outfield, hours before the Mets faced the White Sox on Wednesday afternoon. In one day, he’ll be throwing a ball to a batter for the first time in three months.

The left-handed starting pitcher will throw live batting practice at Citi Field on Thursday, Mets manager Carlos Mendoza told reporters. Manaea, who has been sidelined since spring training with a right oblique strain, will throw “20 to 25 pitches.”

Center fielder Jose Siri, who is rehabbing a broken leg, will participate in the batting practice session along with some players from the Single-A Brooklyn Cyclones.

Out in the outfield during pregame drills, Manaea had a very brief, casual catch with a member of Mets personnel before he headed back into the dugout. After throwing a couple of live BPs, he’ll start a rehab assignment and likely make his season debut toward the end of June. The 33-year-old returned to the Mets this offseason on a three-year, $75 million contract, but he has not pitched this season.

Mendoza also said right-handed pitcher Frankie Montas (high-grade lat strain) will make his second rehab start with the Cyclones on Thursday. Montas, who has struggled with injuries in recent seasons, joined the Mets in December on a two-year, $34 million contract, but he, too, has yet to make his debut with the team.

Right-handed pitcher Paul Blackburn (knee inflammation) had his Tuesday rehab start rained out and moved to Wednesday. It will likely be his last minor league appearance before he re-joins the Mets for his first appearance of the season.

Mendoza said on Wednesday that they’ll potentially use Blackburn as a sixth-man option upon his return. The Mets have a 10-day game streak that begins Friday against the Rockies at home and continues into a West Coast trip to Los Angeles and Colorado. Blackburn’s name will be “in the conversation” to fill that role, Mendoza said.