Wayne Rooney, Ryan Giggs and Paul Scholes are unavailable for the Group C clash at the Mestalla but Mata said the La Liga leaders were ready for a typically resilient performance from the three-times European champions.
"British teams are very physical and the pace of the games is much faster than in Spain," the World Cup-winning Spain international told a news conference on Tuesday.
"In physical terms, we'll have to be at our peak," he added. "But we also have to stick to our football philosophy and keep possession of the ball and hopefully that will be enough."
Valencia began their Champions League campaign with a comfortable win over Bursaspor, thrashing the Turkish champions 4-0 away as United were held to a 0-0 draw at home by Scottish side Rangers.
IMPRESSIVE FORM
Mata has been in impressive form this season to help Unai Emery's side to the top of the domestic standings, while United have been inconsistent and twice had to come from behind to salvage a 2-2 draw with Bolton Wanderers on Sunday.
Mata said Giggs, a fellow left-footer, was one of his boyhood heroes and he was disappointed not to face the 36-year-old Welshman.
"Ryan Giggs has been a player I have liked very much since I was little," he said.
"He is a big loss because of his professionalism and experience but for sure whoever takes his place will do their best. They'll be missing important players but I think they have a big enough squad to cope."
Valencia coach Unai Emery had words of praise for his United counterpart Sir Alex Ferguson, saying the 68-year-old was an example for all coaches to follow.
"I don't know him very well personally but I know his background, career and the trophies he has won," Emery said.
"He is a model for any coach around the world and you can learn a great deal from him.
"We always show great respect for every team but showing respect is very different to fear. We respect Manchester United and their players but we don't have the slightest fear of any opponent."
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