United meet Mourinho's former club in the European Super Cup.
"I think Jose [Mourinho] is already thinking about the final, and has been since Real [Madrid] won the Champions League," the Spaniard admitted.
"The coach wants to win the trophy whilst in charge at United and although Zinedine Zidane had an incredible year in charge, we will try to create problems for them."
The Red Devils midfielder has been visiting Real Oviedo's soccer campus during his time off and described last season as a good one for everyone involved.
"We played very well in the [Europa League] final against Ajax, we won and that has now given us the path into the Champions League." Mata continued.