The 23-year-old signed for the Blues for ?23million towards the end of the summer transfer window and now Mata is excited about returning to the Mestalla Stadium and is hopeful for a rousing reception from the home supporters.
Mata spent four years at the La Liga outfit, making over 100 appearances where he established himself as a regular first-team player as well as winning an international call-up for Spain, so he expects the reunion to be quite emotional.
He told the Daily Star: "It is going to be a very special and emotional match for me playing so soon after leaving Valencia.
"But my priority now is to win for Chelsea. But I will try to be very respectful if I do score and not celebrate.
"The fact of the matter is that I was there for four years and had a wonderful time.
"Everything was very positive and I had great team-mates there with whom I still keep in touch. Even though we will be rivals shortly, I am still going to do the best I can."
Andre Villas-Boas' side started Group E with a comfortable 2-0 win against Bayer Leverkusen while Valencia opened with a goalless draw at Genk.
Attacking
And Mata is hopeful Villas-Boas will allow him a free role in Spain, which he is thoroughly enjoying.
"He tells me the attacking style he wants me to use and to have greater contact with my team-mates," he said.
"He wants me to be involved in passes and setting up goals. He also wants me to score goals.
"When you are behind the strikers your role is to set up goals and provide those passes, but also to score as well.
"It all depends on the game. I might start on the wing but I can move further inside. It depends how the game pans out."
Source: Team Talk
Source: Team Talk