[To qualify for a particular team's 'sleeper' one must have ended the season on that team's final roster, even if they received no playing time with that team, and could not be ranked among the Top 60 Yankees prospects]
Triple-A Scranton: 1B, Mike Ford: This undrafted free agent signing out of Princeton back in 2013 continues to fly seriously under the radar despite boasting some of the best plate discipline in all of minor league baseball. He didn't actually get any playing time in Scranton last season but he ended the season on the roster and immediately grabs the top 'sleeper' spot over the likes of shortstop Cito Culver and outfielder Mark Payton. Ford is undersized over at first base, standing just 6-foot-0, and it's a major reason he hasn't been nor ever will be considered a top prospect. But there is some serious thunder in his swing and the kind of swing that is tailor-made for Yankee Stadium. Throw in some consistent hitting ability and the kind of discipline that can draw more walks than strikeouts, it's not far-fetched to envision him making a big league impact if given the chance.
Double-A Trenton: RHP, Travis Hissong: With left-handers Caleb Frare and Evan Rutckyj on the final roster there's no shortage of solid 'sleeper' candidates. However, both Frare and Rutckyj are former Top 50 prospects so we're going to go with Hissong here to be not-so-safe. Like Ford he's an undrafted free agent signing who has done very well for himself number-wise at the minor league level to date. Forget for a moment that he went a combined 6-1 with a 1.88 ERA over three minor league levels last year with more strikeouts than innings pitched -- the fact he sits 92-94 mph with two average or better secondary pitches and can throw strikes with all three puts him squarely above average stuff-wise and yet from a profile standpoint he gets seriously underrated. There's some back-end big league starting potential or more likely long-relief projection but there's still awesome value there from an undrafted free agent.
High-A Tampa: RHP, Jose Mesa Jr.: This former 24th round pick back in 2012 was absolutely on the brink of breaking out in a huge way last season after seeing his stuff finally blossom into any short of resemblance of his father's [former big league closer Jose Mesa. Not only had he posted a solid 2.97 ERA with 48 strikeouts in 30 innings for low-A Charleston before his promotion to high-A Tampa but his stuff was flat-out sick, seeing his fastball balloon to 95-98 mph, and seeing all three of his secondary pitches [slider, changeup, and curveball] mature into viable above average or better offerings. A reported elbow injury derailed him by season's end and it killed his high-A numbers. Should he return healthy at some point soon, however, and show the same kind of stuff he had in Charleston, he's a legitimate big-time 'sleeper' prospect.
Low-A Charleston: RHP, Hobie Harris: In case some pundits didn't notice, a lot of no-name arms saw significant velocity and stuff spikes pitching in Charleston last year, including this former 31st round pick in 2015. Harris, another power arm from the University of Pittsburgh, saw his velocity spike to the 93-95 sitting range last season after sitting mostly 91-93 mph the year prior and his top-end velocity topped out at 97 mph pitching for coach Justin Pope last year. Armed with both a good curveball and splitter too, while it's tough to carve out a niche in the now pitching-rich Yankee farm system, Harris has the stuff to compete with anyone. Don't be surprised if he sneaks his way up to the big leagues at some point down the road.
Short-Season Staten Island: RHP, Brian Keller: Last year's 39th round pick out of the University of Wisconsin-Milwaukee has a ton of fans in the coaching staff already, thanks to a advanced repertoire of four big league pitches he can throw for strikes and command. The velocity on the fastball sat mostly in the 90-93 mph range in his debut season last year but a lot of team insiders believe there could be a Harris-like velocity jump in his first full season this coming year. Combining that with three secondary pitches that already show big league average or better potential could put him squarely on the map in the not-so-distant future. Watch out, he's a breakout candidate.
Short-Season Pulaski: RHP, Daniel Alvarez: Right-hander Juan Jimenez might be a better 'sleeper' choice given the fact he's 23 years old and hasn't pitched much above the short-season leagues yet -- and with a mid-90s fastball he's certainly a qualified candidate -- but we'd like to go with a little more youth here. The 20-year old Alvarez has numbers on his side to be one of the better prospects [13-4, 2.48 career ERA] but his fastball only sits in the 88-90 mph range so he hasn't garnered a whole lot of attention from scouts. Throw in the fact that there might not be much projection left to increase his velocity considering he's already a full 6-foot-3, 230 pounds, he isn't a big projection guy either. But the curveball is a legit plus pitch, the changeup is coming along, and he can throw strikes. He doesn't have to throw mid-90s to be a great prospect but even just another couple of ticks could change his stock completely.
Gulf Coast League Yankees East: OF, Christian Andrade: We could go with right-hander Miguel Yajure here, a Daniel Alvarez-like clone from a pitch-ability standpoint, and we'd be pretty well set making that prediction. However, we're going to go with one of the more recent International free agent signings. This Venezuelan native shows some Ramon Flores-like hit-ability in the early going as an advanced bat for a 17-year old and the kind of speed that, while not necessarily profiling in centerfield, could be a useful tool in left field long-term. He does show a bit more power potential, however, as there's a bit more natural loft in his swing than Flores had at the same age too. Not a high dollar sign, he could surprise some folks.
Gulf Coast League Yankees West: C, Jason Lopez: Team insiders are very high on this Venezuelan native's entire game but especially on the defensive side. An advanced catch-and-throw guy with the ceiling to be a plus defender down the road, the Yankees also like his bat too despite him sporting just a .233 average through his first two professional seasons. There have been some Luis Torrens-like comments surrounding him, that's how much they think of his game, and that's not even including some intriguing speed too at a position not exactly known for having any. It may not be long before this 'sleeper' turns into legit prospect.
Dominican Summer League Yankees1: C, Ysaac Pena: Another 2016 signing out of the Dominican Republic, this one has the look of potentially being the 'sleeper' of all sleepers listed here. He's not very big, standing just 5-foot-9 and not exactly busting muscles physically, but yet there's some intriguing power in his swing from the left side and some overall hit-ability that has team insiders already pretty excited about his long-term potential. A converted infielder, he still has a long way to go towards learning the nuances of a defense-first position but he enters the conversion boasting plus arm strength. Watch out, the Yankee coaching staff is already pretty high on him.
Dominican Summer League Yankees2: RHP, Anderson Reynoso: Signed in July of 2015 out of the Dominican Republic, he acquitted himself quite well in his debut season this past year, posting a solid 4.53 ERA and striking out nearly a batter  per inning pitched [53.2]. Not exactly a Top 20 DSL prospect right now [although close], he has some intriguing upside worth tracking. He's still growing [he's up to 6-foot-4 reportedly], he has a fastball that now tops out in the mid-90s, boasts a curveball with plus potential, and a quality changeup in the making. There have been some Ivan Nova-like comparisons stuff-wise and pitch-ability-wise at a similar point in their careers. Like Nova, if he can keep getting better and maintain his strike-throwing ways the Yankees could find quite a 'sleeper' on their hands.