Arizona Cardinals defensive back Tyrann Mathieu has admitted that he was never at full fitness in the 2014 season.

The 22-year-old had a promising rookie season for the Cardinals in the 2013 campaign before he tore his ACL, which hampered his preparations for his second year in the NFL.

Mathieu started just six games for Bruce Arians's men last season, which saw a decline in the level of his play and production on the field, leaving him to concede that he was not recovered from his injury.

"It's been a long time since I've been healthy," Mathieu told the club's official website. "Last year I felt like I took a back seat.

"I played well my rookie year and then last year it was kind of, eh, I was there but I wasn't there. This [year] is more important for me because I really want to let everyone know I'm back and I can still make some plays."

Mathieu has recorded 106 tackles, one sack and three interceptions in his two years in the NFL.