GREEN BAY, Wis. -- Morgan Burnett doesn't know when Sam Shields will rejoin him in the Green Bay Packers' secondary, but he knows this much about his best friend: He hasn't lost his love for the game, and he's not going to stop playing in the wake of the fourth concussion of his NFL career.

"Oh, no. No. No, no," Burnett said Monday afternoon when asked if there was any chance that Shields, who hasn't played since the Sept. 11 season opener at Jacksonville, might walk away from football. "Sam's very passionate about this game. He really wants to be out there."

Shields, who suffered one diagnosed concussion in college at Miami (Fla.) before entering the league in 2010, suffered the first concussion of his NFL career in 2011 and missed one game. He sustained another in 2014 but was able to play the following week. Then last year, he suffered his third in a Dec. 13 game against Dallas, missed the Packers' last three regular-season games and then sat out the team's NFC wild-card victory at Washington before returning for the Packers' season-ending NFC divisional playoff loss at Arizona.

Packers coach Mike McCarthy struck a hopeful chord when the team returned from its bye week Monday, although he stopped well short of saying that Shields would be cleared in time for Sunday night's game against the New York Giants at Lambeau Field.

"Sam, he's improving. I know the break was good for him. He was able to go home," McCarthy said. But while four other key defensive players -- including Burnett, who didn't play in the Packers' Sept. 25 win over Detroit because of a groin injury -- returned to practice, Shields, who visited a concussion specialist almost two weeks ago, did not.

"I think our medical staff has done a great job," McCarthy said. "I think Sam has an excellent support group, not only his family and a number of people as far as his agent [Drew Rosenhaus]. No stone has been left unturned. I think we have a very good handle on why and how [the concussion symptoms have lingered] and really the process for him to come back."

Burnett, who joined the Packers the same year as Shields and has been his closest friend on the team ever since, has been part of that support group.

"Anytime you have any injury that causes you to miss time, it's frustrating. Because it's out of your hands," Burnett said. "But he's in good spirits. We talk every day. But we talk about things outside of football -- to get your mind off of the game. He always checks how my kids are doing, I always ask how his family is doing. So that bond is deeper than just teammate. That's a brother bond there.

"I don't know what he's going through. Sam can only determine how he feels. I respect him like a brother, I care about him like a brother. Whatever decision he rolls with, I know he's going to make the best decision for himself and his family. I support him 100 percent."