The Goats will be missing more players from an already-thin squad after parting ways with four squad members.
Casillas arrived on loan from Chivas USA's parent club in February 2013, and the 19-year-old midfielder played in five games with the team.
Velázquez joined Chivas in February 2013, after spending most of his career with Mexican First Division team Puebla F.C. With the Goats, the veteran started 12 games and scored one goal.
Bolaños had been with the club since January 2012, when he arrived on loan from Ecuadorian club Liga Deportiva Universitaria de Quito. The 23-year-old scored three goals in 29 games played.
Courtois was the longest-serving member of the four, having arrived in August 2011. In three seasons with the Red-and-White, the veteran midfielder played in 33 games.