Past and possible injuries aside, the one place where the Mets have the most uncertainty moving forward is in the middle infield. It is widely known that Jose Reyes is in the final year of his contract, and whether Sandy Alderson will or is able to re-sign him remains up in the air. As of right now, the second base position remains up in the air for this season, and there are certainly no guarantees that whoever wins the opening day job will be able to secure the position for the entire season and into the future. With potential holes to fill, let’s take a look at the middle infielders the Mets have in the upper levels of the minor league system that could be fighting for a spot on the roster a year from now.The most logical internal replacement if Jose Reyes is not retained is Ruben Tejada. At the tender age of 20, Tejada played 78 games in the major leagues last year, playing both second base and shortstop. Despite the open competition at second base this spring, the Mets new front office is determined to keep the young Tejada in the minors throughout the year, declaring early on that he would be the everyday shortstop for AAA Buffalo. The hope is that Tejada’s bat develops with a full year in AAA to the point where he can contribute to a major league lineup, and not be a one-dimensional player. Defensively, Tejada is already a great major league shortstop, showing off a brilliant glove during his time last year. While he’ll never be like Reyes offensively, Tejada is great defensively and could become a reliable contact hitter, and at this point the best option the Mets have to replace Reyes if they have to in 2012, and could also be an option at second base if Reyes is retained.The hopeful choice to rise above the clutter that is piling up at second base this spring training is Reese Havens. Havens is one of the top prospects in the Mets organization, but his way up the minor league system has been slowed by injuries. With a healthy 2011, which he should start at AA Binghamton, Havens could progress to the point where he would be the obvious choice to be the opening day second baseman next year. He is a former shortstop who has transitioned well to second base, and will have the benefit of Wally Backman and Tim Tueffel tutoring him at the position while in the minor leagues. At the plate, Havens has more power than the average second baseman, and has also displayed good discipline and a good understanding of the strike zone. With solid defense and the powerful bat he could potentially provide, Havens is not only the ideal internal option to take over the second base job in 2012, but a dangerous weapon that could give the Mets one of the best infields in baseball, but only if he can overcome the injuries that have plagued his career thus far.A candidate that could fill either position up the middle is Jordany Valdespin, who is more likely to end up at second base in the long term, but has played shortstop during his time in the minors. Valdespin possesses the type of speed and athleticism that has the potential to play at the top of the lineup. He doesn’t have power, but can accumulate singles and infield hits. His problem has been being patient at the plate and drawing walks, something he’s never been able to do, and if he can’t learn to do it, his on-base percentage will never be high enough to hold down a full-time job. He will also need to learn how to steal bases, in order to harness his speed into a weapon that can enhance his value. The Mets added him to the 40-man roster this past offseason, so either he’s in their plans for the future or they feel he’s worth keeping around. With improvement in his on-base percentage this year, Valdespin could get into the mix at second base next year, or at least use his versatility to carve out a niche as a utility player.Josh Satin is a player on the periphery of the Mets second base situation, but could play his way into the conversation by this time next year. Terry Collins has stated that second base is an offensive position, and if he stays true to those comments then Satin would seem to fit the description. Satin hit .311 with 12 homeruns and 39 doubles between advanced A and AA last year. If he continues hitting like that and adjusting quickly to new levels he could find himself in the equation next year. He is not a gifted defensive player and has been working to learn new positions in hopes of becoming a utility player, which may be his best chance at playing in the big leagues; however, second base is his natural position, and with the future at second base for the Mets so uncertain, it would be foolish to count Satin out.Obviously, it’s too early to discount the Mets current competitors for the second base job, as Daniel Murphy, Brad Emaus, or Justin Turner could all prove themselves worthy of being the Mets second baseman for the long term. However, it’s more likely that whoever claims the job this year will be a one season stop gap, which means that during next offseason the position will be as wide open as it is now, only the Mets will have guys they have brought up in their farm system competing for a spot on the major league roster. The uncertainty of Jose Reyes’s future with the Mets beyond this year adds another dimension to this issue, which makes having options in the minor leagues all the more important.