Athletic have struggled to adapt in Europe this season and sit bottom of Group H after three games with just one point, while Porto are top with an unbeaten record.
Since Porto won 2-1 when the sides met last month, Athletic have secured successive La Liga victories, including a 1-0 success over Sevilla on Sunday.
However, defeat on Wednesday, combined with a win for Shakhtar, would eliminate Valverde's side with two games to play, something he is keen to avoid.
"We have more obligations than Porto to this game," he told a media conference on Tuesday. "We know we need to win to keep having chances in the competition.
"We are in the process of finding the balance that allows us to achieve results [in the competition]. I hope that the team will match the opposition."
And Valverde knows the support of the home crowd in the San Mames can help his side in their quest for a first group stage victory.
"The support of the fans is very important," he added. "It gives us a lot, but they do not play.
"We know we have to be better than Porto on the pitch."
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