Now in his second stint as the team's head coach, Shell acknowledged it wasn't easy when it came time for him to hang up his cleats for the last time.
''That's a difficult thing for guys that have been playing this game for a long time,'' Shell said. ''For me, staying close to it as a coach gave me a chance to wean myself away from the game. Some guys can't step away from it. They still want to play and they still think they can play but their bodies won't allow them to do it.
''You get to a point where you're just too old to play the game. You can't play anymore. It happened to me.''
The 35-year-old Kennedy played 12 years in the NFL and earned three trips to the Pro Bowl, all of them while in Oakland. He retired following the 2003 season and joined the NFL Network as an analyst.
His weight ballooned after retirement but he apparently had been working out recently in an effort to get back into the NFL. Kennedy reportedly is also scheduled to work out for the Washington Redskins this week and the Arizona Cardinals.
''It's tough getting the body prepared to play the game,'' Shell said. ''If you haven't played it in a couple of years you knew it was going to be a heck of a transition for him to get his body ready to do that. Your body starts barking at you, saying, 'Wait a minute, we haven't done this in a while. What are you trying to do to me?' It's a tough thing.''
The Raiders held just one practice Wednesday and will work out Thursday before packing for the trip to Ohio for the Hall of Fame game.
Shell had not yet worked out the quarterback rotation for the game against the Eagles but said most starters would only play minimally.
* Linebacker Robert Thomas injured his knee in practice Wednesday and had to be taken off the field. The extent of the injury is unknown.
* Rookie wide receiver Will Buchanon, who played at USC, is having an outstanding camp thus far. He made several leaping catches in practice Tuesday then followed that up with a jumping 45-yard reception over safety Jarrod Cooper and cornerback Dennis Davis.