Unai Emery’s men will be seeking to overturn a 3-1 loss they suffered in the first leg in France and Koscielny believes Sunday’s win against Manchester United in the Premier League will give them a huge boost.
"It is a big European night at the Emirates against Rennes and we need the place to be rocking,” he told the club’s official website.
“Our defeat in the first leg in France was disappointing after playing for more than 45 minutes with 10 men. The third goal we conceded, on a counter attack, hurt. However, we are still very much in this tie.
"Like in the United game, our team spirit will be one of the keys too. We need to have that warrior mentality, play for each other and believe in one another."