De Rossi replaced Mourinho as coach earlier this week.
Ahead of his first game in charge against Hellas Verona, De Rossi said: "I sent him a message, he wrote to me when I accepted SPAL, it was my right and proper gesture. I can't concentrate on other things now, I have to concentrate on Roma because in recent days I've also had to do many other things, the uniforms, the contract, other non-football things. I can't wait to be able to think only about football."
On his first days of training, De Rossi said: "I encountered some problems while watching the matches. Roma didn't play badly, they played some games badly, others well. Roma had alternations on the pitch.
"We're coming up with some ideas, obviously I can't tell you here, it would be disrespectful. The players are strong, I knew it, and you are impressed live. I was used to playing with strong players. I was amazed by (Nicolo) Pisilli, he is a young man, a boy, a child but he impressed me."