By pre-season, you mean the actual pre-season games, right?
It's just a little confusing because of the wording in the alert messages.
I also got an e-mail that said:
"Your team has too many players
If you do not bring your team down to the maximum players by the next sim, your coaches will automatically cut your players for you."
I thought the "next sim" was tonight (or early tomorrow), which is what concerned me.