Team officials told the New York Post that the Yankees want to limit Joba Chamberlain to about 140 innings and will start him off in the pen as a result.
140 seems an awfully small number, but it's more realistic considering that they'd love to have him pitch an extra 30 or so during October. If they really want to keep him down that far, then he'd have to spend at least two full months in a setup role. Still, the Post believes the Yanks would still go with Chamberlain in the rotation initially if someone gets hurt during spring training. As is, Ian Kennedy would be the fifth starter.
Source: New York Post
Related: Ian Kennedy
This is something I thought might happen and it scares me because it's very likely that he'll be the only competent arm in that bullpen outside of Rivera. So after 2 months of the season, they aren't going to detract from their bullpen to put Joba in the rotation and we'll never get to see him as a starter.
Although we can't really rely on Mussina staying healthy (or good) in the rotation, so who knows how this will work out.