TEMPE, Ariz. -- In what, by all accounts, will be a rebuilding season for the Arizona Cardinals, their defense was going to be the one steadying factor in a sea of new faces and playbooks.

It was supposed to be the one area that was getting a quick fix following a dismal 2018.

It was supposed to carry the Cardinals until the offense under first-year coach Kliff Kingsbury and rookie quarterback Kyler Murray found its footing.

It was supposed to be all that, until Thursday.

That’s when news broke that Cardinals eight-time Pro Bowl cornerback Patrick Peterson was suspended for six games for violating the NFL’s performance-enhancing drug policy, according to ESPN NFL Insider Adam Schefter. Peterson has already dropped his appeal of the suspension, according to Schefter, who also reported the Cardinals knew of Peterson’s pending suspension before the draft, which is likely one of the reasons Arizona drafted University of Washington cornerback Byron Murphy with the first pick of the second round.

They were getting ready for life without Peterson.

For the Cardinals' defense, losing Peterson for six games might be the worst blow they could've received this offseason. Arizona used free agency and the draft to restock a defense that was once a top-five unit with the likes of cornerback Robert Alford and linebackers Terrell Suggs and Jordan Hicks. The defense didn’t need much work to get back to what it once was, and the pieces Arizona added accomplished that.

But that plan only works when Peterson is accounted for. He was as critical a piece as anyone on the roster -- maybe the Cardinals' most important defensive player.

Regardless of all the issues surrounding him -- from his trade request midway through last season to his problems this offseason with the front office over something that was said to him -- Peterson was a pillar of Arizona’s defense. The season opener at home against Detroit will mark the first game he will miss in his career.

And with the Cardinals hiring Vance Joseph to be their defensive coordinator this year, they returned to a 3-4 scheme, which Peterson thrived in under former defensive coordinators Todd Bowles and James Bettcher. Expectations were high for Peterson, who manned one of the few positions Arizona never had to worry about -- never even had to think about.

Peterson is widely considered one of the top corners in the NFL. He takes away half the field. He often plays on an island, which allows the Cardinals to game plan and get creative with the 10 other players. His throw rate (how often he was targeted) last season was 10.4 percent, according to NFL Next Gen Stats, the fourth-lowest rate among corners with at least 300 snaps.

Quarterbacks fear Peterson. They didn’t want to throw to him or anywhere near him. That frustrates him. He wants the action and has long felt he wasn’t getting the respect he deserved because no one tested him, and as a result his interception numbers were consistently low.

That was the ultimate sign of respect from a quarterback.

Now the Cardinals won’t have his ability against the likes of Detroit’s Matthew Stafford, Baltimore’s Lamar Jackson, Carolina’s Cam Newton, Seattle’s Russell Wilson, Cincinnati’s Andy Dalton (and receiver A.J. Green) and Atlanta’s Matt Ryan (and receiver Julio Jones) over their first six games.

Peterson’s likely replacement is Murphy, a talented young corner. Quarterbacks will pick on him because of his youth and go after him the way they used to against corners who lined up opposite Peterson. It could lead to a long six weeks for a secondary that once had so much promise.

If this year’s Cardinals already didn’t have so much to figure out, Peterson’s suspension gives them another major hurdle to overcome.