And if Jackson can't stay healthy, things really get dicey.
"It's one of those things where you work on it in the preseason as an emergency-type situation, and now it's an emergency," Kuhn said. "We need to go out and perform."
"The one-back position carries fullback and halfback responsibilities, and we're prepared to go forward," McCarthy said. "So I don't look at us as one play away from being locked into playing with a different position at the (halfback) position of our offense."
Jackson is confident he can carry the load. The second-round pick out of Nebraska in 2007 has become an effective third-down back.
"They've always been telling me you're one play away and just be ready," Jackson said. "Obviously, I've been doing that for three years now, a long time coming. And it's here, and I'm taking advantage of it."
"He is actually someone that we were looking at through training camp," McCarthy said. "I just had a chance to watch him today. Very explosive, instinctive, definitely has a very strong, quick lower half. Everything we saw on film was validated today. He is a young player, and I think he will be a good fit for us."
"I think," Rodgers said, "when you give a guy a change of scenery, and a guy like that who might feel like he has something to prove, and surround him with two guys, (linebacker Desmond) Bishop and myself, who have played with him, I think that can only help him feel comfortable and see a lot of production."
Packers general manager Ted Thompson isn't known for making splashy moves out of desperation and doesn't like to part with future draft picks. So, for now, it's Jackson, Kuhn and Nance.
Grant was not present when the team's locker room was open to reporters Wednesday. On his Twitter account, he said he thought he had a chance of returning later in the season but understood that the Packers needed the roster spot.
"You can sit here and say he would have been ready for the playoffs, based on someone else that went through it in the past," McCarthy said. "You look at past injuries, but it's all about the individual. It's about the doctor's opinion of the specific injury."
He missed four straight games in 2007 with a shin injury, two games in 2008 with a wrist injury, and the first four games of last season because of an ankle injury.
Beyond that, Jackson hasn't carried the ball more than 75 times in a season, raising concerns about how much he will have left in December, when Grant has seemed to be at his best?
"This offseason I trained my body to handle the load, and obviously it's here right now," Jackson said. "So we'll see."
Copyright 2010 by The Associated Press