HOUSTON — Some of the injured Mets are on the mend.

Of the five veterans who started the season on the injured list, three have resumed baseball activities and one will start Monday. However, aside from Paul Blackburn, returns aren’t exactly imminent from left-hander Sean Manaea, right-hander Frankie Montas, second baseman Jeff McNeil and catcher Francisco Alvarez. Still, all are progressing at an expected rate, which is positive.

Manaea (right oblique strain) has been playing catch from 90 feet for about a week, and continues to do so in New York. Alvarez (left hamate bone surgery) had his stitches removed Monday and was able to do receiving drills Saturday with what manager Carlos Mendoza said was a softer ball. The backstop is working on catching and receiving, which Mendoza said is a good step.

Manaea and McNeil are aiming to be back in mid-to-late April, but the Mets are taking a cautious approach with both of them. Like Manaea, McNeil is also dealing with a right oblique strain, and with how easily those can be re-aggravated, the Mets are hesitant to commit to an April return for them until they start ramping up their rehab and meeting important benchmarks.

“Oblique injuries are tricky, I don’t want to put a firm time table on this,” Mendoza said Saturday at Daikin Park. “On the position player side of things, they have to start facing live pitching. Same thing with pitchers, not only throwing their bullpens, but they’re facing hitters. We’ll see how it goes when they get to that phase, and then we’ll have a better understanding when they’re going to be back.”

Blackburn (right knee soreness) will start throwing Monday.

CENTER FIELD SWITCHING

Tyrone Taylor started in center field for the Mets in the first two games of their season-opening series against the Houston Astros this week, but in the series finale, Mendoza is turning to Jose Siri. Coming into spring training, Siri was hoping to hit for more contact, and while he did that at times during Grapefruit League play, he still had the same problem that has plagued him at the plate for years: strikeouts.

The Mets are willing to live with some of them because they saw the ability to make adjustments at the plate when he wasn’t getting the contact he wanted with a leg kick.

“Yeah, we know they’re swinging missing there, but I think he’s made some good adjustments,” Mendoza said. “The leg kick, you see him more spread out, more on his leg, trying to be shorter to the ball. And hopefully you see those results here in the regular season.”

The Mets like Siri’s ability to run the bases. The speedster can take extra bases on hits or steal them after reaching. Siri can be somewhat wild on the basepaths but the Mets think his work with Antoan Richardson will help reign him in and reduce his caught-stealing rate.

OH BABY

Francisco Lindor is on alert with his wife, Katia, due any day with the birth of the couple’s third child. Two years ago, Lindor somewhat infamously opted not to take a day off after the birth of their second daughter in New York, Amapola, and if the timing is right, he may not have to miss another day for their first son. Katia is at their home near Orlando, and the Mets head to Florida on Saturday night for a series against the Miami Marlins that begins Monday. Lindor is hoping Katia gives birth on Sunday, when the team is off, but the Mets are prepared for their star shortstop to leave if need be.