By Matt Williamson | ESPN Insider

Despite receiving a gift on Sunday afternoon when the Philadelphia Eagles fell 48-30 to the Minnesota Vikings, the Dallas Cowboys couldn't capitalize. Everyone has seen or heard how Dallas blew a 26-3 second-half lead to fall 37-36 to the Green Bay Packers on Sunday, and everyone has subsequently blamed Tony Romo and/or coach Jason Garrett. They both played their role -- according to ESPN Stats & Information, the Cowboys entered this game with the league's second-lowest running percentage (37) when holding a lead, and that pass-happy preference was inexcusable Sunday -- but they're not solely responsible for the problems in Dallas.

In truth, most of the blame should go to the defense, which is staking its claim as the worst in the league. What does this team need to do to fix this unit this offseason?

Before delving into everything that has gone wrong, it's only fair to point out Dallas has suffered an inordinate amount of injuries, especially along the defensive line. The Cowboys franchisedAnthony Spencer last offseason, but he has missed most of the season with a knee injury. Jason Hatcher has been a superb player up front, but he, too, has missed time. At linebacker, the Cowboys on Sunday were without Bruce Carter and Sean Lee, their best defensive player and a premier linebacker. They also lost Justin Durant to a hamstring injury and Ernie Sims to a hip injury, which utterly depleted their linebacking corps as the game progressed.

However, the real issue with this defense lies in the initial decision to switch from an attacking 3-4 defense to Monte Kiffin's 4-3 Cover 2 scheme. This was foolish to begin with, as they have asked too many players at every level of the defense to do things at which they do not excel. Now they must course correct to help rehabilitate the players they've put into a compromised position.

For example, Dallas paid a major premium to land Brandon Carr and draft Morris Claiborne, both press man cornerbacks, and then switched to much more of a zone-based scheme that generally doesn't need as many high-end assets at the cornerback spots. Claiborne in particular has really suffered with the scheme change.

There is sure to be a change at defensive coordinator this offseason, but the bigger issue for Dallas is that this franchise must pick a scheme and stick with it. Dallas needs to hire the best coordinator available, implement his scheme and stay with it for the long term. Their personnel right now is somewhat in no-man's-land and isn't suited a great deal better for either a 4-3 or 3-4 defense. That will give them flexibility in the process, but once that decision is made, commit.

Dallas does have some players on defense it can build around, but the scheme will dictate which players will return the most on a future investment.

Let's start with the assets in hand. Upcoming free agent Hatcher is someone they should do everything possible to keep regardless of scheme. He proved to be a very good three-technique tackle in Dallas' 4-3 this year and also could excel at end in a 3-4. He should be a building block for this defense, but of course, he also won't be cheap to retain. Spencer was a 4-3 defensive end in college and the Cowboys projected him there this year. A good run-stuffer for his size, Spencer would probably do fine in such a role, but he is a more proven commodity as a 3-4 outside linebacker, and to me, that is his best position. Maybe his price tag has come down now with his injury, but edge players of his magnitude are always in demand around the league.

Dallas also has building blocks at the second level in Lee, Carter, Claiborne and Carr. Lee is one of the best tackling linebackers in the league and Carter is a great coverage LB as well. They would fit well as inside 'backers in a 3-4 or with Lee in the middle and Carter on the weak side in a 4-3. Getting Claiborne's career back on track has to be a massive priority for this organization over the offseason. Next year's defense will vary its  coverages, but going to more of a man-based coverage system would be prudent with either a three- or four-man defensive line.

Regardless of the system, defensive line and safety are priority areas for the Cowboys this offseason. If they stick with a 4-3, defensive tackle becomes an immediate need, but so does defensive end. DeMarcus Ware isn't getting any younger and has had some injury issues this season. Adding three quality 4-3 linemen through the draft and free agency would be ideal, as would retaining 4-3 DE George Selvie, whose contract is up. Even when healthy, the Cowboys were light on quality 4-3 defensive tackles and had very few players on the roster that fit the prototype for ends in this scheme.

At safety, Barry Church has played well, but J.J. Wilcox has struggled in coverage and Jeff Heathis not a player who should be getting the majority of snaps for a good NFL defense.

If the Cowboys hire a 3-4 coordinator, they need to find a true nose tackle that demands a double-team in the run game. This is of paramount importance, especially from a run-stopping perspective. If Spencer leaves via free agency, Dallas would need to find an outside linebacker to play opposite Ware, as well as maybe Ware's eventual successor. And even if Hatcher is retained, defensive end would remain a need.

Cap constraints are going to be a big problem for the Cowboys this offseason, and keeping their own like Hatcher and Spencer might be difficult in itself, so the draft will be the most likely route for Dallas to improve this defense, as well as sprinkling in some bargain free agents to plug holes.

Dallas remains very much in the playoff picture and finishes the season on the road in Washington and then hosts the Eagles in Week 17. Sunday was just the Cowboys' second home loss of the season, and the divisional crown should come down to that Week 17 matchup. But even if the Cowboys do make the postseason, they aren't liable to go far with an ailing and overmatched defense. There is enough pressure on Romo to be perfect every time out. Dallas needs to revamp its defense this crucial offseason if it wants to be a playoff contender in the future.