The Patriots ventured into the 2014 season with very little depth and were forced into a mid-season trade for Jonathan Casillas. It doesn't look like there will be a similar issue this upcoming year.
Jamie Collins and Dont'a Hightower will return and should be better than ever with full seasons of All Pro caliber play under their belt (they both tied for the non-existent 3rd Team All Pro distinction). Jerod Mayo is a key player that will be returning from injury. This gives the Patriots a trio of quality starting linebackers.
The returning depth consists of special teamer Chris White, and practice squad yo-yos Deontae Skinner, Darius Fleming, and Eric Martin. Cameron Gordon and James Morris will be returning from the injured reserve to try and make an impact, with Morris considered a favorite of the coaches.
The Patriots signed Jonathan Freeny, a Rutgers graduate who has spent the past four seasons as the Dolphins special teams ace. The 6'2, 250 lbs linebacker shouldn't be considered a challenge for a starting role, but he proved valuable depth for Miami over his tenure.
New England added even more depth through the draft, although neither player should be considered a roster lock. Matthew Wells, the 6'2, 222 lbs speedster, will have the opportunity to effectively take Jonathan Casillas' role on both the defense and special teams due to his coverage ability. Linebacker Xzavier Dickson is larger, at 6'3, 260 lbs, and could possibly find his way as a back-up to Hightower.
The key addition has to be third round pick Geneo Grissom, whom I believe will be considered a linebacker by the coaching staff due to their additions on the defensive line. While the Oklahoma graduate was inconsistent in his play because the coaches changed his position every single week, he flashed ability all over the field. Bill Belichick was downright giddy when discussing his potential, so expect him to play all over the formation.
With the team featuring the sub-package with just two linebackers for the majority of the snaps, it could be argued that Mayo will be considered the top depth at linebacker. However, the one time the trio of Mayo, Collins, and Hightower were healthy last season (week 1), the Patriots opted to play all three for the entire game. Look for Grissom to play the top back-up, and expect White and Freeny to fight for the same roster spot, while the final roster seat designated for linebackers will go to the last man standing from what should be an entertaining camp battle.
Regardless of who remains, it's clear that the Patriots have the ability to rush the quarterback with any of their linebackers. Collins and Hightower were two of the most effective blitzing linebackers in the entire league, and Mayo had developed tremendous timing for shooting up the A gap. Grissom offers a ton of promise. Matt Patricia and the coaching staff will absolutely supplement the pass rush of the defensive line with intermittent attacks from the second level to keep the offense on their toes- and to force errant throws into the secondary.