From FAQ Thread
Originally Posted by Deathless Mortal
What's the deal with top30 players in challengers this year? Do I accept them or not? Question goes for both singles and doubles..
Top 30 players in the singles entry rankings can't play them, except during the Davis Cup and Grand Slam second weeks and when there are no ATP tournaments played.
They are allowed to play challengers in these weeks as late entries (LE), but they are not able to be seeded (qualifying or main draw).