Kyler Murray is ready to start the season, but his backup is not.

The Cardinals placed No. 2 quarterback Colt McCoy on injured reserve on Wednesday with a calf injury suffered Monday. McCoy had been dealing with an arm issue through much of training camp, but coach Kliff Kingsbury said that was healed. Now McCoy must miss at least the first four games of the season.

To take his place on the roster, the Cardinals promoted Trace McSorley from the practice squad to the 53-man roster. They also re-signed QB Jarrett Guarantano, who was with the team through the preseason, to the practice squad to fill McSorley's spot.

"It's unfortunate," Murray said. "It was kind of starting the week off on a downer, someone getting hurt, someone you care about. On his birthday, it's tough.

"But it's good. Trace is good, he's ready to go. I'm focused on executing on Sunday."

The team also signed cornerback Corey Ballentine to the practice squad. Ballentine has spent time with the Lions, Giants, Jets, and Falcons. To make room, the Cardinals released wide receiver Jontre Kirklin from the practice squad.

Losing McCoy may not make a major impact assuming Murray stays healthy, although McCoy did lead the Cardinals to a 2-1 record last season when Murray was out because of an ankle sprain. McSorley played the vast majority of the snaps in the preseason for the Cardinals -- neither Murray or McCoy appeared in a preseason game.

The Cardinals returned to the practice field Wednesday. It will also be the first day of the official injury report.