Keith Srakocic/Associated Press

Nobody is worried about the Pittsburgh Steelers offense.

Potential future Hall of Fame quarterback Ben Roethlisberber is coming off a career year in which he led the league in passing yardage and ranked third with a passer rating of 103.3, reigning receiving yardage leader Antonio Brown was a first-team All-Pro in 2014 and emerging running back Le'Veon Bell led the conference in rushing yardage.

Plus, the rebuilt offensive line was ranked seventh by Pro Football Focus in terms of pass-blocking efficiency.

As a result, the Steelers ranked second in total offense, seventh in points scored, second in time of possession and first in yards per play. And there's no reason to expect much to change on that side of the football in 2015.

Steelers offense, 2014 Category Total Rank Points/game 27.3 7th Yards/game 411.1 2nd Yards/play 6.2 1st Time of poss. 32:24 2nd Pro Football Reference

And yes, that's enough to keep Pittsburgh competitive in an era driven by offensive production. But the Steelers still haven't won a playoff game since 2010, which means they can't afford to take steps backward on either side of the ball.

That's why it was so important that the franchise locked in one of its most important defensive players long term by giving defensive end Cam Heyward a new six-year, $59.25 million contract, according to the Pittsburgh Post-Gazette (h/t ESPN's Adam Schefter).

Heyward, who is just 26 and is coming off a season in which he had a career-high 7.5 sacks and 35 tackles in 16 starts, would have been eligible for free agency next offseason. And losing a guy who in 2014 was graded by PFF as the fifth-best pass-rushing 3-4 defensive end in the game was not something Pittsburgh could afford.

PFF: Top pass-rushing grades for 3-4 defensive ends, 2014 Player Grade 1. J.J. Watt 91.9 2. Sheldon Richardson 24.7 3. Jurrell Casey 21.2 4. Jason Hatcher 18.3 5. Cameron Heyward 17.4 6. Muhammad Wilkerson 11.5 7. Calais Campbell 11.3 Pro Football Focus

Not when you consider the state of this defense.

The Steelers ranked below the middle of the pack last season with 23 points and 353.4 yards allowed per game. They gave up more passing yards than all but five other teams, they recorded fewer sacks than all but six other teams and they ranked in the bottom 10 in the takeaway department for the fourth consecutive year.

Fewest team takeaways since 2011 Team Total Steelers 76 Saints 78 Raiders 81 Jets 82 Colts 84 Pro Football Reference

And then they lost key contributors Troy Polamalu (retirement), Ike Taylor (retirement), Jason Worilds (sudden retirement), Brice McCain (free agency) and Brett Keisel (released), all five of whom started the majority of the team's games in at least one of the last two seasons.

In fact, 2015 will mark the first time since 2001 in which Pittsburgh will enter training camp without the reliable Keisel at defensive end. And with legendary defensive coordinator Dick LeBeau gone, they'll have a fresh face running the defense for the first time in over a decade.

Even before those losses, Heyward stood out in a big way. He was tied with Worilds for the team lead with 7.5 sacks (no small feat for a 3-4 end) while recording the team's highest defensive PFF grade by a huge margin.

PFF: Highest-rated Steelers, 2014 Player Grade 1. Ben Roethlisberger 29.0 2. Cam Heyward 24.6 3. Le'Veon Bell 23.8 4. Antonio Brown 23.4 5. Kelvin Beachum 21.7 Pro Football Focus

Gone are the days when the Steelers gave opposing offenses nightmares. Former Defensive Player of the Year James Harrison is still kicking around, but at 36 he was the second-oldest regular defensive position player in the league last season. And veteran linebacker Lawrence Timmons is coming off a career year, but even he is entering his ninth season, leaving Pittsburgh with a severe lack of defenders in their so-called prime.

Heyward is an exception.

Speaking of age, Roethlisberger is 33. Far from done in quarterback terms, but he's closer to the end than the beginning.

If Pittsburgh is going to capitalize on these last few years of the Roethlisberger era—and the offense should indeed continue to light it up—it absolutely cannot risk losing any more ground on D. That's why it's so important that the team has taken care of a key defensive contributor like Heyward well before the open market could have come for him in 2016.

Brad Gagnon has covered the NFL for Bleacher Report since 2012.

Follow @Brad_Gagnon