Barco, 20, has four goals and one assist in eight league appearances. He suffered his injury when kicked in the knee by a Columbus player in the U.S. Open Cup.
De Boer said that Villalba (knee) and Bello (adductor) are on similar timelines of recovery, but didn’t provide a return date.
Villalba, 24, has one goal and three assists in 11 appearances. He suffered his injury in the game at New York Red Bulls on May 19.
Bello, 17, has yet to play in a league game this season.
“Still a lot of games coming up,” de Boer said. “If you are going to put them in, they have to be 100 percent. You don’t want them to fall back directly.
“We are not rushing. We won’t them back soon because of injuries we have right now. Still, main target is always the health of the player. You gain nothing when he’s back for one game and then four weeks out.”