GREEN BAY -- Call it the Jordy Effect.

The Green Bay Packers didn't just lose their top wide receiver when Jordy Nelson suffered a season-ending knee injury in a Week 2 preseason game against Pittsburgh.

They also lost a beloved teammate whose absence is still something the Packers are trying to get over psychology as the regular season approaches.

"It took the air out of the team. There's no doubt about it," Packers head coach Mike McCarthy told FOXSports.com earlier this week. "When something like that happens, guys are worried about him personally. It definitely affected the sideline to see it.

"I think it also tells you what people think of Jordy, number one, and how important he is in our program."

McCarthy acknowledged the emotional impact of Nelson's fluky injury -- he was hurt when his feet hit the Heinz Field turf on a catch attempt without contact from a Steelers defensive player -- resulted in "a little bit of carryover" during last Saturday's lopsided loss to Philadelphia.

Green Bay eliminated any potential injury risk to Aaron Rodgers by resting their star quarterback. The Packers, though, still received a major scare when wide receiver Randall Cobb hurt his shoulder after landing awkwardly on the sideline trying to snare a Brett Hundley pass on the game's third play.

FOXSports.com reported last Tuesday that Cobb, who is set to assume Nelson's spot as Rodgers' top receiving target, is expected to play Sept. 13 in the regular-season opener at Chicago. But the fact Cobb's health was in jeopardy cemented Rodgers' strong belief that preseason games are largely "meaningless," which is the sentiment he publically expressed after the Nelson injury.

"It's tough because (Nelson) is such a great guy and teammate," Rodgers told FOXSports.com in a one-on-one interview. "His play on the field is exceptional. He does things that you just can't teach out there.

"You can't replace him with one guy. It's just not possible. You just have to have everyone else lift their level of play and try and make up for the loss, if that's possible. But you don't get better losing a guy like Jordy Nelson. You just try to get back to where you were when you had him."

That is where the Packers are turning their focus with the preseason having ended and preparations for the Bears game about to begin in earnest.

"Right now, it's an adjustment period," Packers fullback John Kuhn told FOXSports.com. "Guys are kind of finding their roles. But it won't even take until game time. It will take until that week of practice. We'll have a couple of extra days and guys will know right away what their responsibilities are and expectations for them."

McCarthy is counting on the importance of starting the season right and beating Chicago to get guys out of any remaining funk.

"You can't play like that," McCarthy said. "You're either on or off. If you're one of those guys who can't do that, it's probably not going to work out for you here."