The French side were beaten by a second-half Aritz Aduriz goal at the Stade Velodrome last Thursday and followed up that result with a disappointing home draw against St Etienne on Sunday.
But while Mandanda admits the task facing his side is hard, he says they have got over their recent setbacks and will travel to Bilbao fully confident of turning the tie around.
Mandanda told the club's official website: ``We're aware that we lost the first game and we know what we're facing tomorrow.
``We can't be satisfied with the current results but the game against St Etienne is in the past and there are great things waiting for us if we are able to reverse the trend.''
Marseille right-back Brice Dja Djedje will miss out with a thigh strain against opponents who also go into the game on a downer after losing last Sunday's Basque derby to Real Sociedad.
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