Luiz has returned to Girona on a season-long loan after last term's success.
Carcel told Mundo Deportivo: “The possibility of him coming back to Girona was complicated. I wanted Douglas from minute one, but I was aware that it would be complicated.
“I went to see him personally to convey to him my feelings and what we wanted.
"He was not 100%, clear, but the desire to show his football have been key."