Mathieu made his first appearance of training camp Wednesday morning after missing the first six practices of camp and getting to the team hotel Tuesday night. Saints coach Dennis Allen said they were able to talk at the hotel and that Mathieu appeared to be in "good spirits."
The 30-year-old Mathieu did not participate in 11-on-11 or 7-on-7 drills but went through the team walk-through and did individual drills with the defensive backs.
"He's anxious to kind of get back here and get started," Allen said. "We'll go through a little bit of a ramp-up period with him, kind of let him get his feet up under him, but man, to have a player of his decorated ability back in the building is a positive."
On Thursday, Mathieu spoke to the media for the first time since his return to the team on Wednesday, praising the support he has received from his coaches and teammates and saying he'll go through a ramp-up conditioning period as he gets back into football shape.
"Everyone was really supportive, teammates, former teammates," Mathieu said. "Lot of different people just being supportive. Obviously that was a great feeling, to have that support. ... I'm sure at some point I'll be more transparent about the first six days of practice, but more important I'm just happy to be back and around the guys. I'm feeling good, I'm in great spirits, really healthy. Everything that's important, it's going good. I'm just in a good place and just all about ramping it up and getting back into it."
The offseason addition of Mathieu to the Saints' secondary was met with much fanfare in New Orleans, where Mathieu grew up and played in high school before starring in college at LSU. The nine-year NFL veteran agreed to a three-year, $33 million free agent contract with the Saints in early May.
Mathieu was raised by his grandparents in New Orleans then became a star football player and track athlete for St. Augustine High School. He maintained deep ties to the city, enhanced through his charitable endeavors and football camps in the area.
He also has deep ties to LSU, where his tenacious play over two seasons earned him the nickname "Honey Badger." As a sophomore in 2011, he was a Heisman Trophy finalist and won the Bednarik Award as the nation's top defensive player. But his college career was cut short when then-Tigers coach Les Miles dismissed Mathieu in the summer of 2012 for repeated drug test failures.
Mathieu spent time in a Houston rehabilitation program, but it wasn't until he was drafted by the Arizona Cardinals in the third round in 2013 that he put his life together. Mathieu became a dependable defensive standout for coach Bruce Arians and has since added two All-Pro nods with Kansas City to go with one earned in Arizona. He also has been named to the Pro Bowl each of the past three seasons.
He wound up playing five seasons for the Cardinals before a year with the Houston Texans. He signed with Kansas City as a free agent for $42 million over three years and immediately became the quarterback of the Chiefs' defense, often relaying signals and directing the pre-snap alignment of defensive teammates.
ESPN's Katherine Terrell and The Associated Press contributed to this report.