Campbell, who had been the starting quarterback of the team for a year and a half, missed the end of the 2011 season with a broken collarbone.
It was always unlikely that Campbell would return to the Raiders, since the team needed to reinforce the fact that Palmer is the starting quarterback.
The problem now lies in the fact that Oakland have few options if Palmer fails.
When Campbell went down last season, the Raiders made a desperate move to trade for the former Cincinnati Bengals quarterback. The team gave up a first-round pick and another conditional pick, showing that this was not just a late-season fill-in.
It is now Palmer's team, for better or worse. Last season, the quarterback threw 16 interceptions and only 13 touchdowns in 10 games. The team went 4-6 with him under center, compared to 4-2 prior to his arrival.
An entire offseason training with the team will certainly help, but retaining Campbell would have provided the club with a certain level of insurance.
Considering he agreed to be a backup to Jay Cutler with the Bears, it would not have been out of the question for the veteran to return in the same role in Oakland.
The Raiders need to find another veteran in free agency to be the No. 2 quarterback, just in case Carson Palmer is not what he used to be.