ALAMEDA -- Hue Jackson and the incoming general manager are going to have a pressing issue on their hands this offseason when it comes to their running back stable.Michael Bush, who rumbled for a career-high 977 yards while starting nine games, will be an unrestricted free agent.Darren McFadden, who is a unique talent and one of the most explosive running backs in the game when healthy, cannot stay healthy."Well, it's a concern, but again, you've still got to look at how your team is set up," Jackson said Monday in his season-ending media conference. "Would I love to have Michael Bush back? Yes. Are you kidding me? The guy is tremendous. But Michael Bush is going to have some opportunities himself. Sometimes youre not in control of that, and I respect that. I think Michael loves it here and loves playing for the Raiders and being a part of this organization, but I think any young man in these situations, they're going to do whatever they think is best for themselves and their families."McFadden, meanwhile, has missed three, four, three and nine-plus games in his first four NFL seasons. He sprained his right mid-foot on the Raiders' opening drive against Kansas City on Oct. 23 and never returned, leaving gaping hole in Oakland's offense.So, is McFadden being so injury-prone a concern, since the Raider cannot depend on him for a full season?It's a concern," Jackson said. "Me talking to him, it's a concern of his, too, because he wants to be out there with his teammates competing and playing and helping contribute. Again, this was an unusual year -- not an offseason and going right to training camp and obviously him getting injured early in training camp and starting the season and, boy, he started the season like gangbusters. He was rolling pretty good and then all of a sudden here comes the next injury, and then we didn't have him anymore."And I know everybody said that's been his history. Hopefully we'll get over the hump. And I know it's been foot issues, per se. I know he's going to do his part, to do everything he can to make sure he has an opportunity to play 16 games, because that's what we need him to do. We need him to play 16 straight games to help us earn a 17th."