Stamford Bridge will host the crunch clash in the battle for a top-four spot and Spurs will be hoping their talisman Bale, the PFA and FWA player of the year, can make the difference.
Mata, who was nominated for the PFA award himself, is in no doubt who the Blues must keep an eye on in midweek.
"Obviously, it's a vital game for both teams and we'll have to watch one of the best players in the world in Gareth Bale," said the Spain international, quoted in The Sun.
"He is in amazing shape and proves to be a decisive player for Spurs almost every week. I congratulate him for all his recent awards.
"We now play against Tottenham on Wednesday which is going to be a final again. It's going to be tough but I think we can make it and seal our place in next season's Champions League."
Chelsea will go six points clear of Tottenham with just two Premier League games remaining if they can win the match.