The Bundesliga club tackle the Spaniards in San Sebastian in their final Group A fixture needing a win to progress to the Round of 16.
However, their fate also rests on the Manchester United versus Shakhtar Donetsk clash at Old Trafford with Leverkusen requiring United to avoid defeat to the Ukrainians.
Nevertheless, South Korean ace Son is targeting a victory for die Werkself after they managed to knock off Borussia Dortmund on the road on the weekend.
"Every game's important both for the team and myself, but admittedly there's a lot on the cards for the club in that one," he told Bundesliga.com.
"We should try and focus on ourselves and not look at the Manchester United against Shakhtar Donetsk encounters.
"We have every chance of winning if we produce a performance like we did against Dortmund, and if we also get a bit of luck, then we'll progress."
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