Based on the status of fellow halfback David Johnson, this does not come as much of a surprise.
Johnson had been nursing an ankle injury in the lead-up to his team's Week 7 matchup with the New York Giants this past Sunday. Johnson played all of three snaps in the win, carrying the ball just once for two yards before exiting.
Ajayi has not played in the NFL since October of last year, when he appeared in four games with the Philadelphia Eagles and totaled 184 yards and three touchdowns on the ground before suffering a torn ACL.
He has not been with an NFL team since.
The 26-year-old, who played his collegiate football at Boise State, was originally selected by the Miami Dolphins in the fifth round (149th pick overall) of the 2015 NFL Draft.
Ajayi spent the first two-and-a-half years of his career with the Dolphins, making the Pro Bowl in 2016 after racking up 1,272 yards and eight scores while averaging 4.9 yards.
He was then traded to the Eagles midway through the 2017 campaign and proceeded to help Philadelphia win its first Super Bowl, tallying 408 yards and a touchdown while registering 5.8 yards per attempt in seven games with the club that season.
The Cardinals have won three straight and are now 3-3-1. They are very much alive in the NFC playoff picture, but, obviously, if Johnson is out for any duration of time, Arizona is going to need to help in the running game.
Chase Edmonds provided that for the Cardinals against the Giants, but the Cards may want some insurance in the form of someone like Ajayi.