Valencia were drawn with Chelsea in Thursday night's Champions League group stage draw, along with Bayer Leverkusen of Germany and Belgium's Genk in Group E.
The Blues are now scheduled to play in Valencia on September 28 in the second round of group fixtures which would be just over a month after Mata made his £23.5 million switch to the Barclays Premier League team.
"Had we known it, we would have put a clause in the contract, so he did not have to play against us," Llorente joked, after the draw was made.
"It is a very difficult group, but we are hopeful about our chances. However, we have to stay positive as we avoided other big teams, like Manchester City or Borussia Dortmund."
However, Valencia coach Unai Emery was happy enough that the club's fans would get one more chance to see their former hero Mata play at the Mestalla one more time.
"The draw has been a little bit devious in putting Valencia and Juan Mata's Chelsea in the same group," Emery told UEFA.com
"It will be something special for our fans to see Juan playing at Mestalla in a different shirt. Everyone who has shared a dressing room with him has learned from him as he is a great footballer.
"I wish him all the luck in the world in his new adventure, except of course when he comes up against us."
Valencia kick-off their Group E campaign with a visit to Genk on September 13.
Champions League Group Stage
|Group A||Group B||Group C||Group D|
|Bayern Munich||Trabzonspor||Manchester United||Olympique Lyonnais|
|Manchester City||LOSC Lille||FC Basle||Dinamo Zagreb|
|SSC Napoli||CSKA Moscow||Otelul Galati||Real Madrid|
|Group E||Group F||Group G||Group H|
|Valencia||Arsenal||Zenit St. petersburg||BATE Borisov|
|Bayer Leverkusen||Olympique Marseille||Shakhtar Donetsk||AC Milan|
|Racing Genk||Borussia Dortmund||APOEL||Viktoria Plzen|