While they do not have many holes on their roster, the Super Bowl champion New England Patriots must do a majority of their damage this off-season through the draft. The Patriots must find a way to bring back key players like Darrell Revis, Devin McCourty and Shane Vereen with an already shaky salary cap situation. Because of this, the free agent pool is going to be very limited to New England.

With that being said, the Patriots can always make key improvements to their team through the draft. While there have been plenty of misses through the years, Bill Belichick and his staff have traditionally done very well at the draft, especially when it comes to finding values in the later rounds.

If the Patriots want to be serious repeat contenders, they must continue to find late round gems in the 2015 version of the draft. Here are five sleeper prospects who Belichick and the Patriots would be wise to target after the early stages of the 2015 NFL Draft.

David Johnson, RB, Northern Iowa

In his four years as a running back for the University of Northern Iowa, David Johnson rushed for 4,682 yards on 866 carries (good for a 5.4 yards per carry average) and 49 touchdowns. He was also a massive weapon for the Panthers in the passing game with 141 career receptions for 1,734 yards and 14 touchdowns. Johnson leaves UNI with nearly the entire rushing record book and even some receiving marks. While it was at the FCS level, Johnson has been one of the most productive running backs in college football over the last four years.

Johnson is a very powerful runner who rarely goes down on first contact. At 6-foot-2, 229 pounds, Johnson has a thick and muscular build, and runs very well for a man of his size. He is a dangerous weapon as a receiver out of the backfield, and that is something that is rare for a powerful runner.

With Vereen and Stevan Ridley hitting free agency, the Patriots are likely to add a running back in this class. If they decide to pass on the position in the first couple of rounds, Johnson could be a great value for the team, and a versatile weapon for Belichick in the third to fifth round range.

Jaquiski Tartt, SS, Samford

Jaquiski Tartt Samford 2015 NFL Draft
Tartt (6) gang tackles the ballcarrier with his teammates.
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Jaquiski Tartt is an athletic traditional safety who was a very successful basketball player in high school. He started his football career as a senior in high school, and his skills are very raw because of it. That being said, his late start in the game suggests that Tartt has better days ahead of him once he refines his skills on the field.

He is a very aggressive player who excels in run support from the safety position. While his coverage skills certainly need some refinement, he is a physical hitter who will punish receivers coming over the middle of the field.

Patrick Chung and Duron Harmon fit the mold of a traditional strong safety for the Patriots right now. While it may not be a huge immediate position of need, neither Chung nor Harmon represent much future upside. Tartt is a potentially dynamic player who could stand some development. He is a great special teams player, who could thrive in that role immediately in New England, and the team could allow him to develop at the right pace defensively.

Aundrey Walker, OG, USC

Throughout his career at USC, Aundrey Walker showed great versatility by lining up all across the offensive line. Nobody loves versatile prospects as much as Belichick, and the Patriots sure could use a talent infusion on the interior of their offensive line.

Walker projects to be a guard at the next level, but his experience playing on the outside and at center is certainly valuable. He is a strong run blocker with good power. Walker has long arms and solid athleticism for a man of his size, which allows him to be good in pass protection, and there is upside for him to get better in that department as well.

Walker is unlikely to be taken before the sixth round, but he could be a late-round gem for the Patriots at a position of need.

Xavier Williams, DT, Northern Iowa

Xavier Williams UNI 2015 NFL Draft
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Another interesting prospect from Northern Iowa in this draft is defensive tackle Xavier Williams. At 6-foot-2, 325 pounds Williams has the size to be a force to be reckoned with at the next level. While he lacks consistent pass rush abilities, Williams is a very athletic player for a man of his size, and is able to get to the quarterback at times.

He does show the potential to be a powerful run stopper, and he does well in that department at times, but he will need to get stronger to be a consistent performer at the next level. By all accounts, Williams is a very hard worker and strong leader, something that the Patriots’ organization puts a high premium on.

Vince Wilfork is unlikely to be with the Patriots for more than one more season. Currently, they do not have anybody in the pipeline to replace him. Williams would give them protection at the nose tackle position, and has the athleticism and ability to eat up blocks to play the five-technique at times as well. He would be a great third day pick by the Patriots.

Tony Lippett, WR, Michigan State

Tony Lippett Michigan State 2015 NFL Draft
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The Patriots have never been able to develop a big target at the wide receiver position for Tom Brady. Typically, smaller slot receivers are the ones that have had the most success in the Brady era. If given the opportunity, Tony Lippett would have a good chance to buck that trend.

At 6-foot-3, 193 pounds, Lippett has the size that scouts crave at the wide receiver position. While he does not have huge breakaway speed, Lippett is quick in small spaces and fast enough to create separation. He has incredible footwork and is a very good route runner. Lippett is a strong receiver who uses incredible balance and strong hands to catch many balls in traffic.

Lippett is a solid receiver prospect who has very few holes in his game. He could step right in immediately and be a solid contributor offensively while representing plenty of upside. Lippett also started at cornerback for Michigan State down the stretch. That sure seems like something that would have Belichick’s attention.