PORT ST. LUCIE, Fla. -- The New York Mets celebrated Johan Santana's birthday Wednesday morning with a quick team-wide gathering in a conference room and a cake with "34" on top.

The southpaw already had realized this spring training that age is catching up with him as a pitcher.

Santana has not been atop a mound in seven days, since he tried to ramp things up for a second time in spring training and his shoulder again told him he was not quite ready.

He does not officially rule out breaking camp with the Mets, but the math almost assuredly dictates Santana will open the season on the disabled list, where he finished last season.

Left-hander Jonathon Niese has been tabbed as the alternate Opening Day starter. And right-hander Jeremy Hefner is being stretched out to fill Santana's rotation void until the southpaw is ready.

"As far as setting dates, I'm not to that point," Santana told ESPNNewYork.com.

Mets manager Terry Collins acknowledged Santana is "not too close" to returning to a mound.

"Each and every day we'll see how he feels," Collins said. "When he thinks his arm -- the strength -- is there to get on the mound and throw a bullpen, he'll do it. But he's the only source we have as to how he feels. We checked with him this morning and found out what he was going to do today. And tomorrow, we'll leave tomorrow until when I see him tomorrow and see where we stand."

After each of Santana's first four seasons as a Met, he was rehabbing from surgery during the offseason -- from a procedure to repair torn meniscus cartilage in a knee during the 2008-09 winter, an elbow cleanout the following year, then shoulder surgery for the next two winters.

So this offseason Santana took it easy from an offseason throwing program, which he said came as the result of consultation with the team.

"They wanted me to rest," Santana said. "And they told me to relax and go home and just take some time off. And that's what I did. And then I started getting back in my conditioning and all that, but not into pitching."

Upon arriving at camp and trying to fire things up on a mound, however, Santana's now-34-year-old body did not cooperate. Twice he has been backed off from mound activity during spring training while trying to build up more shoulder strength.

"When we do something like that, we're trying to test it out, see how it feels," Santana said. "And then we go back to strengthening my shoulder and spending time in there rehabbing and making sure the strength is back. It's just taking one step at a time, working and making sure every day I feel better. That's pretty much what I'm doing right now."

Santana appeared to bristle when Mets officials publicly griped that he arrived at spring training not in pitching shape, particularly the day one tabloid had the back-page headline: "Shape Up!" He had not given a full interview in two weeks.

But Santana was cheerful Wednesday and indicated he had no interest in getting into a war of words with the organization. He has spoken with general manager Sandy Alderson to smooth things over.

"They talked about all kinds of things," Santana said about the public criticism. "They make comments and everything. I've been here every single day. I've been doing everything the way they asked me to. I've been working out, keeping track of everything.

"It's just that when you talk about pitching, it's a totally different thing. Pitching takes time, especially when you come back from some time off. My last game was in August. To get on a mound in February, you're talking about six months. To go out and pitch, that takes time. You have to build that up -- anybody. You go around any team, any pitcher, it takes time to build everything up.

"I want to make sure that whenever that day is, I'm ready to go and good to go for the whole year -- and not just good for one game, or so you have a story, or so anybody else has a story, and then two weeks later they have to shut me down. I don't want that. I want to make sure that whenever I'm on the mound, I'm on the mound for good."

Asked if this was just a matter of age and not related to more shoulder problems, Santana said: "I don't know. The last couple of years have been tough for me -- rehabbing, surgery and all of that."

Santana had expressed strong interest in representing Venezuela during the World Baseball Classic. Given the shoulder weakness, that turned out not to be feasible. But his intention to participate is an indication that Santana was caught off guard by how long it would take his body to get ready for the 2013 season.

"At the time I felt good," Santana said. "And as we started working and working, I felt like I wasn't there. It's things that you don't know until you get here.

"As you get older, you have to work more. There's no question about it. But you have to know yourself very well. That's what I do. I'm listening to my body the whole time. When you need time, you take time to make sure you move forward. You don't want a step back.

"It's things that you don't know. You have to go through it to see where you're at. That's what we were doing -- working, following the program, everything that I was told. And we keep track of everything. It's just that I knew when I was throwing my bullpens and it was time to face some hitters, it wasn't there. So you go back to work out and long-toss and try to get strength in your shoulder."