Valencia coach Mauricio Pellegrino concedes a loss to BATE Borisov on Wednesday would make it tough to advance in the Champions League.
BATE, Bayern Munich and Valencia are equal on six points after three games in Group F, while Lille, who have suffered three defeats, are seemingly out of contention for a place in the knockout phase.
Valencia head into the home match full of confidence, having accounted for the Belarusian champions 3-0 in the reverse fixture last month.
"I think this is a very important match, due to how open the group is," Pellegrino said.
"If we won that would be a very firm step forward ahead of the next games.
"If we lost, to qualify would be very complicated.
"A draw would leave us more or less like today but if we win, that would be a massive step ahead."
Pellegrino could hand Ever Banega his first start in the competition this season, with the Argentine midfielder easing his way back after eight months on the sidelines with a broken ankle.
"He has been out for a while so he needs to get back on track, little by little," Pellegrino said.
"He is getting in shape again so we just need to give it time for him to be as his best, like with any other player; we just need to measure what's best for the team."