Ahead of tonight's clash with Roma, Sarri was full of praise for the Argentina striker.
He said, "He is fine, even today he was particularly alive in training.
"He is an important player, for reasons of balance he plays with the other two or with one of the two. Recently he has less frequented the penalty area but is a player of an unusual calibre.
"Douglas Costa? He is doing well at the moment. He's had a heavy workload. We must be careful because he is at risk of injury. The extremely positive aspect is that he has found continuity in training."