The French side were beaten 2-1 at the Stade Velodrome by Napoli and are rooted to the bottom of Group F, having also lost to Arsenal and Borussia Dortmund.
Ayew has told his teammates to focus on Ligue 1 for now and hopes that his side can secure a place in the Europa League by finishing third in their Champions League group.
"It's another defeat. There's nothing to say. There's no point repeating the same things. We have to forget this and win on Saturday against Reims," Ayew told reporters. "It's looking very difficult to finish second, but perhaps we can still take third. We have to stop thinking about the Champions League, though. We have two games before our next Champions League match and we have to win those and see what happens after.
"I'm very disappointed. We need to go home, calmly get over this loss and think about the future. We have to lift our heads up again. The way we played in the second half tonight is the way we need to play in the first half of games as well.
"We all have to face in the same direction and show more determination and more desire to play and fight. I'm not worried. When you look at how we ended the match and our second half, there's no reason to be worried. But there's the question of results as well, and that was our fourth defeat in a row."
Marseille host Reims on Saturday.