The Midlands club have to face off against the French outfit again to determine progression.
After winning the first leg 2-1 at home on Thursday, manager Unai Emery knows that a tie on aggregate is very much possible.
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"Difficult match, very tough match," Emery told TNT Sports.
"A tight result and a tight match. We created chances, we conceded some chances. We took advantage today and we knew before the match it was going to be difficult.
"Now again we have to be ready there to play 90 minutes and even extra-time and penalty shootout even because we know now every match that we are playing is difficult.
"It's a good result because we won today. We know it is going to be difficult there but we have to try to get again our position on the pitch, understanding how we play today."