At age 28, when he left the Minnesota Twins to sign a six-year, $137.5 million deal with the New York Mets, optimists had every reason to believe that while it was still relatively early in Johan Santana's career, he was destined for the Hall of Fame.

Optimism is rarely rewarded when it comes to baseball, let alone pitchers. Santana certainly wasn't bad on the Mets, at least not at first -- between 2008 and 2010, the initial three years of the deal, he threw precisely 600 innings of 2.85 ERA baseball, just about the definition of an ace pitcher in the league. Thanks to Tim Lincecum and Brandon Webb he finished third in National League Cy Young Award voting in his first, and best, season in New York.

The NL Cy Young results for 2008 are tragic in a number of ways, looking back now. Lincecum won (he's thrown 383.2 innings of 4.75 ERA ball over the past two seasons), with Webb finishing a fairly distant second (Webb, 30, would throw four innings for the Diamondbacks the following year and never pitch in the majors again). Santana was a bit behind him in third place (over the past three seasons, Santana has thrown 117 innings of 4.85 ERA ball at the MLB level, all of those innings coming in 2012). Then-Phillies closer Brad Lidge came in fourth with the best season of his career (Lidge threw 9.1 innings for the Nationals in 2012 and has not appeared in an MLB game since); C.C. Sabathia finished fifth (he had a downright pedestrian 2013 -- a 4.78 ERA in 211 innings), and Ryan Dempster rounded out the group in sixth (Dempster is now the fifth starter for the Boston Red Sox, and may lose his spot in the rotation this spring after a horribly disappointing end to 2012 and a 2013 almost as unimpressive as Sabathia's).

The oldest of the six was Dempster, who turned 31 that July. Of the others, only Lidge had even turned 30. Lincecum was 24. Yet five years later, only Sabathia was able to even come close to realizing the promise showed in 2008.

Brandon Webb is undoubtedly the most unfortunate of the bunch -- he had six phenomenal years for the Arizona Diamondbacks before his labrum frayed past the point of no return, officially retiring last February with a career ERA of 3.27 (142 ERA+) in 1319.2 IP at the age of 33. Santana isn't far behind, however. Between 2004 and 2008 he had one of the best five-year peaks of his generation, throwing 1146.2 innings of 2.82 ERA ball (157 ERA+) while winning two Cy Youngs as a Twin and finishing at least in the top five in Cy Young voting in every season. For reference, compare that to Clayton Kershaw's line for the last five seasons: 1072.1 IP of 2.43 ERA ball (155 ERA+). Santana during his last four years in Minnesota and his first in New York was arguably a better pitcher than Kershaw has been while he's been dazzling in Los Angeles, putting up a very slightly better adjusted ERA than the Dodger ace in 74.1 more innings pitched. And Santana was only entering his age 29 season when he signed with New York. At six years, $137.5 million dollars -- the last year of the deal being a club option worth $25 million with a $5.5 million buyout -- he should have been worth every penny.

The Mets exercised that buyout on Nov. 1st, 2013, granting the now 34-year-old Santana free agency. I've mentioned before that 2008 was a sort of last hurrah for the Mets in a number of ways, and that was no less true for Johan Santana than it was for the team as a whole. He'd pitch two more seasons of very good, even great work in 2009 and 2010, but 365.2 IP of 3.05 ERA ball in those years -- good for "only" an ERA+ of 131 -- wasn't quite up to the standards Santana had set for himself the previous five. And then in 2011 he only threw five innings of minor league ball, missing most of the year with shoulder surgery.

That was the beginning of the end for Santana the ace. He came back in 2012, supposedly rested and recovered and ready to pitch, but his fastball was now consistently in the upper eighties, when it had hovered around 91 to 92 MPH before, and his breaking pitches didn't have the same snap they used to. His strikeouts ticked up a bit in that final year in New York, but so did his walks; Santana's 7.8 BB% in 2012 is the highest he's ever put up in a full season of work.

One popular theory as to why Santana's 2012 ended in disaster points to the no-hitter he threw as the straw that broke the camel's back, but that's an imprecise reading of the tape. Santana threw the first no-hitter in the history of the Mets on June 1st, 2012, the first start of the month -- and finished the month of June with 39 innings pitched of 2.77 ERA ball. That's almost exactly the same as his ERA for the season up until that point; including April and May, Santana had thrown 98 IP to a 2.76 ERA in 2012. It was July when disaster struck, and never stopped. That month he was only able to make five more starts the rest of the season, only pitched 19 innings across them, and in those 19 innings surrendered 33 earned runs. Considering the surgery he was coming back from and the diminished ability already showing through in his fastball and breaking pitches, the no-hitter was likely irrelevant, especially considering how much better his second half of June was than his first half (even including the no-hitter). Johan Santana's arm -- specifically, the anterior capsule in his left shoulder -- was probably always going to give.

Which brings us to the present, and the news that Johan Santana's rehab is going "better than expected," for whatever degree of "expected" there is for a pitcher who is just now starting to throw off of a mound and who hasn't been clocked on a radar gun yet. One of the biggest signs of very serious problems with the recovery of injured players -- especially injured pitchers, and very especially pitchers with injuries in their throwing arms -- is suffering the same surgery-requiring injury multiple times. Guys like Carl Pavano, who missed time for everything from batted balls to the hand to Tommy John surgery to shoulder problems to falling down while shovelling snow and rupturing his spleen, are a bit rarer than guys like Mark Prior or Brandon Webb, who have the same problem over and over again because the first injury is so bad it compromises their future.

It is possible, if not likely, that Johan Santana's left shoulder is now simply incompatible with the rigors and strains that a full season of MLB baseball will put on it. It is almost certain that the Johan Santana that dazzled the league from 2004 to 2008 is gone, and it's not outside the realm of possibility that even though Santana is not yet even 35, his days as even a league-average starter in Major League Baseball are done.

We'll know more once Santana throws a bullpen for scouts, which should happen sometime this month, probably before the real meat of spring training starts, so that he can get as much time in camp as possible to impress a prospective team. It's very unlikely that Santana would receive anything more than a minor league deal with an invitation, a major league roster trigger and possible incentives similar to the ones Mark Mulder received from the Angels, and it's quite likely that he'll just get a standard NRI. The most interested parties appear to be his last two teams, the Twins and Mets, though most of the Mets' reported interest came earlier in the offseason. The Orioles would also make a certain amount of sense, given how GM Dan Duquette puts his roster together, but so would, e.g., the Yankees if the price was right. That it's highly unlikely Santana will ever again be an effective workhorse in the majors is far, far different from it being impossible -- and just the possibility that he could return to even his 2009-2010 form is enough to get a number of pitching-starved teams interested.

So Johan Santana will get a deal of some sort, and he will probably even pitch in 2014 at some level and for some length of time, though he will not be the ace he once was, just like almost every other colleague of his who received an NL Cy Young vote in 2008. Nearly all of those men -- and perhaps even Sabathia, depending on how 2014 goes -- are now testaments to how fleeting and fragile greatness can be in baseball, and how quickly peaks can fall.