The New England Patriots are World Champions once again after winning their sixth Lombardi trophy in the past 18 seasons. Their focus now shifts to 2019 and defending their title.

As with every NFL team, changes are coming to the Patriots this offseason. Left tackle Trent Brown, the anchor of the Patriots' offensive line that thrived in the playoffs, signed with the Oakland Raiders. Receivers Chris Hogan, Cordarrelle Patterson (signed with the Bears), and Phillip Dorsett are also free agents on that side of the ball. Defensive end Trey Flowers (signed with the Lions) and cornerback Jason McCourty have expiring contracts, while punter Ryan Allen and kicker Stephen Gostkowski are free to hit the open market as well.

Aside from retaining core players from their championship squad, who else will the Patriots chase in free agency? Let's take a look here at four under-the-radar free agent targets for New England.

3. Tyler Eifert

The future of Rob Gronkowski, who is considering retirement, remains a mystery. The tight end's agent, Drew Rosenhaus, speculated that his client may make a decision on his playing status “in the next couple of weeks.”

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Regardless of Gronkowski's plans for 2019, the Patriots need to add insurance at tight end. A player to keep an eye on is Tyler Eifert, who has spent all six seasons of his NFL career with the Cincinnati Bengals.

A former first-round pick, Eifert is a proven offensive playmaker when healthy. He caught a career-best 13 touchdown passes in 2015, his lone Pro Bowl campaign. He has played in only 12 games over the past three seasons, however, and has struggled to stay on the field throughout his NFL tenure, appearing in only 43 out of a possible 96 games.

Tyler Eifert, Bengals
Frank Victores/The Associated Press

The Patriots have successfully revived veteran careers before and Eifert could fit in well in an offense that features its tight ends heavily in the passing game.

Dwayne Allen will remain a fixture in the offense as a pass-blocking tight end, but he can't be relied upon to catch passes at this stage of his career. Assuming health, the 28-year-old Eifert could integrate himself into the Patriots' offense catching passes from Tom Brady, with or without Gronkowski in the lineup.

2. Golden Tate

The Patriots have a lot of question marks at receiver. As previously noted, Hogan, Patterson, and Dorsett are set to become free agents and their statuses are up in the air moving forward.

The open market includes veteran wideout Golden Tate, a one-time Pro Bowler who could be lured to New England if he is willing to agree on a moderate contract.

Traded from the Detroit Lions to the Philadelphia Eagles midseason, Tate logged 74 receptions for 795 yards and four touchdowns in 2018. He remains a strong route runner and is elusive in the open field.

Tate, set to turn 31 in August, is unlikely to command top-notch dollars in free agency. He can still be a dominant force in the passing game though, especially with Brady under center. He could alleviate some of the pressure off Julian Edelman, who carried the bulk of the targets in in the Patriots' Super Bowl run. The Patriots may present Tate with his best shot at getting a second Super Bowl ring, having won one with the Seattle Seahawks in 2013.

1. Brent Urban

The Patriots need reinforcements along the defensive line, regardless of whether they can retain Flowers. Baltimore Ravens unrestricted free agent defensive end Brent Urban might be a player the Patriots go after.

Urban led the Ravens in snaps among defense lineman last season. He started all 16 games and became a strong asset in the NFL's top ranked defense.

After appearing in just three games in 2017, the Ravens signed Urban to a one-year, $1.1 million ‘prove-it' deal before last season. He demonstrated his worth by posting a career-best 27 tackles.

If Baltimore cannot agree on a long-term deal with Urban, the Patriots could pursue the 27-year-old to bolster their defensive front.