I actually think the wording is fine. As JenB points out, the disc is only illegal, if it isn't approved by the the TD at some point in time, after it the legality has been questioned. If the TD approves the disc after the round, the disc was never illegal to use.
However, there is a risk associated with using the disc after it has been questioned, that may or may not have been intentional. If you lose the disc, the TD cannot approve it, and it then becomes illegal, and you risk beeing DQ'ed. If the disc gets damaged to the point where it becomes illegal after it has been questioned, what then?