Mata enjoyed a successful spell at Stamford Bridge with the Blues after moving from Valencia back in August 2011.
However, the Spanish playmaker then ended up leaving the west London side to sign for their Premier League rivals Manchester United in January 2014 after finding his playing time at Stamford Bridge limited under Jose Mourinho.
Mata is now holding down a regular spot in the first team under Mourinho at Old Trafford and is preparing to line up against his old club when Manchester United travel to Chelsea on Sunday afternoon.
And the midfielder has revealed that he still has very fond memories of his time at Stamford Bridge.
Writing in his personal blog, Mata said: “We travel to Stamford Bridge [on Sunday] – a place that’s been very important in my career, as you know.
“That was a few years ago, but my gratitude to all the people at Chelsea for what we had there is still present.”
Manchester United head into the game on the back of their 1-0 victory over Tottenham last weekend.
Chelsea, meanwhile, were also 1-0 winners as they beat Bournemouth at the Vitality Stadium on Saturday.
Chelsea are currently nine points behind leaders Manchester City, while Manchester United are second and five points off top spot.
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