Johnson sustained a freak injury early in the season when he lost part of his fingertip in his side's defeat to the New Orleans Saints.
That injury forced him out of action and as a result rookie safety Mathieu came into the side and impressed, forcing Johnson out of the starting lineup.
"It was a struggle because I didn't think it was going to take so long," Johnson told the club's official website.
"As a leader, sometimes you have to be able to accept the duty that is given to you. No job on the field is smaller than another.
"If it is personally protecting on the punt, getting the last kickoff of the game against the [Atlanta] Falcons, that's just as big of a play as the interceptions."
The Cardinals are 4-4 in their season.