I have a ridiculously similar issue in the post just above yours. There is a slight and important difference though. Tanking a game to get a better matchup happens in real NFL all the time, tanking a game (as with my issue) just in spite of another team does not.
While in terms of sports I think it's fine since real teams do it and it is strategy, I also believe that this is a fantasy game with fantasy rules. This should be fun. With your issue, I say that you need to talk to this guy, but I don't think a commish can do anything if he decides to tank anyways. If this is a friend's league, then he really needs to play it out, if this is a random person league then do whatever is best for your team I guess.
Zito is God in the Baseball Cafe