You have stated that they quit before the championship match, so here are illegal and legal things you should keep in mind :
- If he is not playing, but waiting to play in the final match, it's legal.
- If he is playing in the finals, quits, and if you can prove that he ragequit or just did it to mess with the tourney purposely, it's illegal.
- If he quit, but you cannot prove the previous statement, nothing can be done.
- If he quit for a certain real life or internet connection problem (as in a non purposeful action), that's legal.