Johan Santana delivers a pitch from the mound during a...

Johan Santana delivers a pitch from the mound during a spring training workout at Tradition Field in Port St. Lucie, Fla. (Feb. 17, 2013) Credit: Newsday/Alejandra Villa

PORT ST. LUCIE, Fla. -- Early on a Wednesday morning at an empty Tradition Field, isolated from the bustle of the back fields, Johan Santana threw off a pitcher's mound for only the second time since the Mets shut him down last August.

Manager Terry Collins didn't like what he saw.

"He didn't have the arm speed," Collins said Friday. "You could just tell."

Based on that throwing session, the Mets decided to hit the brakes on Santana. They have pushed back his Grapefruit League debut by as much as two weeks, perhaps putting into question his status as the team's Opening Day starter.

"It's obviously a possibility," general manager Sandy Alderson said of the chance that Santana might not be ready by April 1. "But right now, we're still shooting for Opening Day."

Santana played down the team's concerns about the strength of his surgically repaired left shoulder. Nevertheless, the Mets scrapped his planned Grapefruit League debut next Saturday. Santana won't make his first appearance until sometime between March 10-15.

"It's not a setback at all," said Santana, who is owed $31 million, including a contractual buyout for next season. "It [the shoulder] needs time to build up."

According to Alderson, team doctor David Altchek examined Santana on Thursday and assured the Mets that he had not discovered any structural damage in the shoulder. Nevertheless, the results of Santana's second throwing session prompted the Mets to take action.

"It was a matter of observation and sort of a mutual recognition that maybe things needed to be backed off a little bit," Alderson said. "It's just a matter of building up strength, and so there will be long-tossing before he gets back on the mound. We just expect that his schedule will have been delayed somewhat."

After more than a year on the shelf, Santana made a triumphant return from major shoulder surgery last season and threw the first no-hitter in franchise history. But his return engagement ended in August. Nagging back and ankle injuries -- and concern about the workload on his shoulder -- prompted the Mets to shut him down.

Santana entered the offseason focused on resting his body. He waited until January to begin a throwing program. At the time, he planned to pitch for Venezuela in the World Baseball Classic, which meant he'd accelerate his pitching regimen.

Instead, the Mets denied Santana's request to pitch in the WBC, citing lingering concerns about his shoulder. With that off the table, the Mets implored Santana to ease off his throwing program.

Said Santana: "We're not trying to rush anything."

Notes & quotes: Lefty reliever Pedro Feliciano and outfielder Jamie Hoffman have been sent to New York for what Alderson said are follow-ups stemming from their original physicals. He declined to offer further details, citing privacy issues . . . Jenrry Mejia arrived in camp after a visa issue that had kept him out of the country . . . Wilmer Flores hit a three-run homer off veteran reliever LaTroy Hawkins in Friday's intrasquad game. Jordany Valdespin also hit a solo shot off righthander Brandon Lyon. . . Grapefruit League play begins Saturday against the Nationals and pitching phenom Stephen Strasburg. Top pitching prospect Zack Wheeler is among those scheduled to pitch for the Mets.