TEMPE, Ariz. -- Losing rookie safety Tyrann Mathieu for the season wasn't just a blow to the Arizona Cardinals' secondary, it's a continued decimation of the Cards' 2013 draft class.

Mathieu is Arizona's fourth drafted rookie to suffer a season-ending injury this season, following guard Jonathan Cooper in the preseason and linebacker Alex Okafor in Week 3. Wide receiver Ryan Swope was forced to retire after suffering a concussion during minicamp. Arizona only has four draft picks on its active roster after releasing tight end D.C. Jefferson, a seventh-round pick, in early November.

The Cardinals' four injured draft picks are tied for most in the NFL with the Green Bay Packers and Houston Texans this season.

Cardinals coach Bruce Arians was concerned another rookie was about to be sidelined two weeks ago when rookie running back Andre Ellington, Arizona's second sixth-round pick, tweaked his left knee leading up to the Eagles game on Dec. 1. Arians thought Ellington, who was sidelined for the game, had hurt his ACL. But it turned out to be not nearly that bad as Ellington played Sunday against the Rams.

Arians doesn't expect Mathieu to return by training camp next year, but the other rookies, Cooper and Okafor, are slated to be healthy by July.

“It definitely has got us,” the coach said. “We got lucky with Andre Ellington.

“But, yeah, with Swope and Coop and the rest of them, it's a shame because we really needed them.”