De Roon admitted they have had a 'short holiday', but the midfielder is happy to be back.
“There's a great desire to return, we have had a short holiday, but we are charged and ready to play," De Roon told Sky Sport Italia.
“We have managed to improve every year. First, we thought fourth was the best, then we reached the quarter-finals of the Champions League.
“Castagne left, but we bought four or five players and I have already seen two or three at work, and they are strong," De Roon added.
“Then [Aleksei] Miranchuk will arrive and [Josip] Ilicic could return. We have a strong enough team."