The striker endured a difficult first full campaign at Stamford Bridge following a £50m move from Liverpool.
"I was very happy with Fernando at the end of last season," said Di Matteo. "He was brought in to be a fantastic striker and, hopefully, will be able to fit into our team and show his qualities.
"The price tag comes with the fact he has been superb over the years for the teams he has played for, Liverpool and Spain. So we are very confident in him."
FA Cup winners Chelsea take on Premier League champions Manchester City in the Community Shield later today.