The New England Patriots may be the reigning Super Bowl champions, but even they have work to do.

The Patriots have lost their two best cornerbacks this offseason, Darrelle Revis and Brandon Browner, and defensive captain Vince Wilfork is now with the Houston Texans. The Patriots have some holes to fill on defense and running back.

With that being said, here are five NFL free agents the Patriots may want to consider signing:

1. Terence Newman

There's honestly not a lot of good corners left on the open market. The Patriots recently signed Bradley Fletcher to a one-year contract, but they know gaps still exist without Revis and Browner on the outsides. Terence Newman isn't a shutdown corner by any means, but he is a pretty physical player who can make tackles. The former No. 5 overall draft pick has played with the Cincinnati Bengals and Dallas Cowboys since 2003, and the Patriots have shown a lot of interest in him this offseason.

2. Knowshon Moreno

LeGarrette Blount is a good running back, but he can't carry the load as an "every down back", especially without Shane Vereen, who is now with the New York Giants. In addition to that, Stevan Ridley will most likely not be returning to the Patriots next season because of constant injuries. Knowshon Moreno could be a good, low-cost addition as a part-time back. Although he missed almost all of last season with the Miami Dolphins, he's still a very talented player. In 2013, he ran for 1,038 yards and 10 touchdowns, helping the Denver Broncos get to the Super Bowl. A low-risk investment that could pay off for Bill Belichick.

3. B.J. Raji

It's going to be stunning to watch the great Vince Wilfork play for another team next season other than the Patriots. Wilfork will go down as one of the best run stoppers in NFL history, but he's no longer with the team. Former Green Bay Packers defensive tackle B.J. Raji could be the man to fill that gap. Raji was one of the biggest reasons the Packers won the Super Bowl in 2011 with his abilities at the line of scrimmage. Injuries are a concern with Raji, but the Patriots have to be worried about stopping opposing rushing offenses.

4. Mathias Kiwanuka

Now this could be a very interesting signing for Belichick, who can be a defensive mastermind. The Patriots obviously won't have as good of a secondary as they did last season, so getting to the quarterback will be more crucial than ever. Breaking the bank on Ndamukong Suh wasn't something Robert Kraft had in mind, and who could blame him? Greg Hardy also recently signed a one-year deal with the Dallas Cowboys. But, defensive end Mathias Kiwanuka is available as a free agent. The Patriots have an excellent linebacker core, and the addition of this 32-year-old pass rusher could be beneficial for a very low cost.

5. Ahmad Bradshaw

The Patriots could make a really underrated signing here. Ahmad Bradshaw knows how to win games, and he's a very unselfish player. Twice he was the leading rusher in the Super Bowl, both games coincidentally against the Patriots. Bradshaw won't lead the Patriots to the top-ranked rush offense, but he's a north-style type of runner, and he can perform well in frigid, cold and windy conditions. He doesn't have great speed or athleticism, but he very rarely fumbles (three total fumbles last two years) the ball, and he always gives you positive yardage. Even last season, Bradshaw averaged 4.7 yards per carry.

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