GREEN BAY, Wis. -- Packers cornerback Sam Shields suffered a concussion in Sunday's regular-season opener at Jacksonville, coach Mike McCarthy confirmed Monday after Shields underwent tests.

The concussion is Shields' second in less than nine months and the fourth known concussion of his NFL career. He missed four games because of a concussion late last season and missed one game in 2011. He also suffered a concussion in 2014 but didn't miss any games.

"Any time any of our players is in the protocol and dealing with a concussion, it's a concern," McCarthy said Monday. "That's why we'll evaluate Sam each and every day, and most importantly to make sure he's healthy and goes through the challenges of what he's dealing with."

Packers cornerback Sam Shields was not cleared to play against the Giants this week. He is recovering from his fourth concussion in the last six years. David Rosenblum/Icon Sportswire

McCarthy offered no other details about Shields' condition.

"It's a protocol, and I think they do a great job, particularly our doctors, of taking it one step at a time," McCarthy said. "We definitely are aware of his history, and that will factor in how we move forward."

Shields was slow to get up after he tackled Jaguars running back T.J. Yeldon in the fourth quarter of Sunday's 27-23 win, but he was able to walk off the field under his own power.

Last season, Shields missed the final three games of the regular season as well as the wild-card playoff game at Washington after his head slammed onto the Lambeau Field turf in the team's Dec. 13 game against the Dallas Cowboys.

If Shields is unavailable for next Sunday night's game, the Packers will turn to a trio of young cornerbacks in second-year pros Damarious Randall, Quinten Rollins and LaDarius Gunter.

While Randall played well as the other starter against the Jaguars, Rollins was benched midway through the game in favor of Gunter, who also struggled. Rollins was forced to return after Shields left the game.