Two-time Cy Young Award winner Johan Santana, who is slated to open the season on the disabled list, may not make a quick return to the New York Mets.

Santana continues to be plagued by shoulder weakness and is only throwing on flat ground at 90 feet.

He roughly would need to double that distance on flat ground before returning to a mound for the first time since an ill-fated March 6 attempt. Assuming everything feels OK at that point, he still would need to go through a full spring-training-like ramping up.

“I’ve just got to stay here and work out and get ready,” Santana said Saturday morning. “… I’m making progress. It’s just I don’t know when I’m going to be pitching again. That’s the thing: We cannot think ahead. The way we’re approaching everything is every day make sure we have a good day.”

Left-hander Jonathon Niese will get his first Opening Day assignment for the Mets in Santana’s absence. Right-hander Jeremy Hefner will fill the rotation void.

Santana, who turned 34 earlier this month, is in the final guaranteed season of a six-year, $137.5 million with the club.

He underwent surgery to repair a torn anterior capsule in his left shoulder -- a rare procedure in baseball -- on Sept. 2, 2010 and finally returned to the majors last season. Although he had first-half success, including the first no-hitter in franchise history last June 1, Santana faded badly before landing on the disabled list in August.