GLENDALE, Ariz. -- The "Honey Badger" is about to get his first NFL start.
Mathieu has been a sensation in training camp as he looks to make a comeback after being booted from the LSU team for marijuana use and sitting out football altogether last season.
In his NFL debut in Arizona's 17-0 victory at Green Bay last week, Mathieu had a 12-yard sack, a tackle for loss, a pass defended, two special teams tackles and a 24-yard punt return.
Johnson has a mild ankle and knee sprain, injuries that occurred when he broke up a pass late in practice on Monday.
"We'll be cautious with him," Arians said. "He's having such a great camp."
Mathieu said Johnson is among those who has "shown me the ropes" about playing safety and he wishes him a speedy recovery. When Johnson returns, Mathieu still figures prominently in Arizona's defense in the nickel and dime packages.
He's just making too many plays, knocking balls loose and picking off passes, in practice to not have him on the field.
Arians has noted that the entire Cardinals squad has taken Mathieu under its wing. The coach called the 5-foot-9 player "a lovable kid" who has been "making plays all over the field."
Mathieu, a Heisman Trophy finalist in 2011, was kicked off LSU's team before the start of last season for failed drug tests.
His image and presumably his NFL future took another hit a few weeks later when he and three former teammates were arrested on marijuana charges after police officers found 10 bags of pot and drug paraphernalia in his Baton Rouge apartment.
When he appeared at his introductory news conference with the Cardinals, Mathieu said he wanted to abandon his nickname of "Honey Badger" because of all the problems associated with his time at LSU.
But he's found that fans still love it, shouting it out to him at practice.
Now Mathieu is starting in the second preseason game after missing an entire season of football.
"I couldn't fathom it," he said. "It probably was a longshot, but I'm just putting in hard work, man, and I guess everything's starting to come together for me."
Mathieu said his teammates are telling him to just do his job.
"For the most part everybody's just telling me to play my role [and] everything's going to come to me," he said. "Don't get caught up in the media and all the hype that's going on right now, just go out there and keep doing what you're doing."
When Arizona drafted Mathieu in the third round, it was considered a big risk for the team. From the start, he said, the Cardinals fans showed their support.
Asked what they've said to him, Mathieu said, " 'Good luck', 'I hope you stay clean,' 'I hope you stay healthy,' 'I hope you come here and make plays like you did at LSU." '
That support has only grown through the first few weeks of training camp, not only locally but around the country.
"I think a lot of people kind of jumped back on the bandwagon, so to say," he said, "on Twitter, everywhere, everybody's starting to root for me again, which is definitely encouraging."