TUESDAY, 12:50pm: The Cardinals have placed Mathieu on the injured reserve list, officially ending his season. As expected, the club has added a safety to the 53-man roster to provide some depth, re-signing veteran free agent Chris Clemons, who was cut by Arizona from IR earlier this season (Twitter link link via Urban).

MONDAY, 1:26pm: The Cardinals clinched the NFC West with their victory Sunday night over the Eagles, but that win came at a cost. Head coach Bruce Arians announced today that standout defensive back Tyrann Mathieu will miss the rest of the 2015 season – and postseason – after suffering a torn ACL (Twitter link via Darren Urban of AZCardinals.com).

Mathieu, 23, started all 14 games for the Cardinals this season, spending time at both cornerback and safety. Having already established new career highs in tackles (89), interceptions (5), and passes defended (16), the former third-round pick was one of the key players on defense for Arizona, so his loss will be a crushing one for the team.

Pro Football Focus had Mathieu ranked as the top cornerback in the NFL this season, grading him as the best in the league both in coverage and against the run. Defensive coordinator James Bettcher recently told Albert Breer of the NFL Network that he believed Mathieu should receive consideration for the league’s defensive player of the year award.

The Cardinals were also without Rashad Johnson during Sunday’s win over Philadelphia, so it wouldn’t be a surprise to see the club add another safety to the 53-man roster this week — Tony Jefferson and D.J. Swearinger could see increased roles, with Mathieu headed to IR.