The Gunners suffered a 1-3 defeat in France last week as defender Sokratis Papastathopoulos saw red in the first half of the match. The north London side must score two goals and avoid conceding for them to advance to the next round and Emery stressed for a big atmosphere if the club is to overturn the deficit.
"We need to [focus] on tomorrow and create a very emotional moment in 90 minutes with our supporters. We need to be clear in our minds in the 90 minutes, very fresh and very cool to take the best decisions," Emery told the club's official website.
"I don’t think about [being favourites]. I only want to play the best possible match, doing all we can, with each player and the team."
"In the first game, they beat us and now we will want to show that here it can be different, but with a big respect to them and also knowing we need all the players with the focus and to control our emotions and control the different situations and scenarios that can come in the 90 minutes. This is our way and our match.
"[Rennes] are a good team in a good moment and they have quality with different players. They have spirit and fresh players playing offensively and they are organized defensively. They won against Betis over two matches with a big performance and against us, they showed also they have the possibility to win against us.
"But after this big respect to them, we will try to push tomorrow, starting with our supporters and a big atmosphere helping us. With our gameplan and capacity, we can come back against them."
Arsenal will welcome back Alexandre Lacazette to the squad after missing two matches through suspension.