While linemen competed in full-contact drills the other day, Washington Redskins defensive end Jason Hatcher worked with trainers. He’s still not ready for action. Hatcher had arthroscopic surgery on his left knee June 20, and given the pace of his rehab, the Redskins would be smart to hold him out of preseason games. They can’t play it too safe.

Hatcher is the linchpin of President and General Manager Bruce Allen’s plan to improve a defense that has been among the NFL’s worst the past two seasons. After luring Hatcher from the NFC East rival Dallas Cowboys, the Redskins are banking heavily on him to bolster the pass rush and, in turn, benefit their porous secondary. Why risk their investment — a guaranteed $10.5 million this season — by playing him in meaningless games?

The preseason provides a chunk of the NFL’s massive profits and is vital in helping decision-makers evaluate young players hoping to gain a foothold in the league and established ones trying maintain their standing. Ideally, Hatcher would have lined up with the first-team defense from the outset of camp. Familiarity often helps build cohesiveness.

However, you don’t have to be a sports-medicine professional to tell Hatcher still is not running smoothly. For the Redskins, having Hatcher take it slow in practice is a good start. Eliminating the preseason from his schedule is the next logical step.

At 32, Hatcher is entering his ninth season. Self-starters such as Hatcher don’t need many preseason snaps to get into playing shape and regain timing. Privately, veterans often complain about the length of the preseason. Hatcher, who became a starter in 2011, has logged a lot of miles in his career. Why add more before the games that matter?

The Post Sports Live crew looks at the biggest story lines ahead of Redskins training camp, from the struggling secondary to keeping all of the offensive stars happy. (Post Sports Live/The Washington Post)

Some Redskins observers would argue Hatcher needs to play in the preseason to prepare for the regular season. I probably would agree if camp was still being run by Mike Shanahan, whose training camps weren’t particularly hard, players say. New Coach Jay Gruden has ratcheted up the intensity, so whenever Hatcher is medically cleared to practice, he’ll rejoin a group that puts in a full day’s work.

From the way Hatcher tells it, there’s more than enough time for him to get rolling in practice. He claims he’s “ahead of schedule” but trusts the medical staff to clear him “at the right time.” Behind closed doors, Hatcher has assured defensive coordinator Jim Haslett that the Redskins will consistently pressure the quarterback by rushing just four players.

The inference is clear: With Hatcher on the line, Haslett can commit more players to coverage. That’s a bold statement.

Last season, Hatcher had the statistics to back it up, leading the Cowboys with 11 sacks. He also led all NFL defensive tackles in sacks while playing an interior position in a 4-3 alignment. That’s not easy. Hatcher demonstrated the strength to beat double-teams and the agility and quickness to win one-on-one battles. A team official told me that, based on his 2013 tape, Hatcher was the most impressive free agent defensive lineman the front office evaluated in years.

But here’s the catch: That season was either a breakthrough or an anomaly. Hatcher, who also has played end in a 3-4 front similar to the one the Redskins use, hadn’t had as many as five sacks in a season until getting 11 in a contract year. The question is, in what direction will his career go next?

The Redskins envision Hatcher and outside linebackers Brian Orakpo and Ryan Kerrigan blasting off together. The secondary definitely needs it to happen. In 2012, Washington had the 28th-ranked defense in the 32-team league. Last fall, opponents averaged 29.9 points against the Redskins — tied for 30th in the NFL.

Despite obvious holes, Allen made no major moves at safety. He brought back safety Ryan Clark, who played two seasons with the Redskins earlier in his career and the past eight with the Pittsburgh Steelers. Clark turns 35 in October. This will be his 13th season. At Clark’s age, it would be surprising if he provided a major boost in coverage. To put it kindly, the rest of the safeties don’t inspire confidence.

The Post Sports Live crew explains why no major news out of training camp is good for the Redskins coming off of a 3-13 season. (Post Sports Live/The Washington Post)

In all likelihood, any improvement on the back of the defense must start up front. That’s Hatcher’s area. But until the regular season begins, he should stay out of it.