United were 3-1 ahead at one stage and the draw leaves their hopes of reaching the round of 16 hanging by a thread.
Fernandes said, "It's really hard. We conceded really bad goals. We have to take control of the situations in all of them.
"We were on top of the game twice and we had far too many chances to have the game closed. We were not clinical enough.
"I have nothing to explain. We concede the two goals and there's nothing we can do now. Obviously we could have done better with those two goals but it is what it is.
"Every time we conceded a goal we had many chances to score again. At the end of the game we had four chances. We have to lift our heads up and try to get the best players in the best positions and not take chances ourselves. We need to put the team first. It was mistakes by ourselves on the goals we conceded.
"It's too hard to be honest, I don't want to be too negative. But what we have been doing in the Champions League is not enough. It is not the first game we've had like this. We have to secure the result.
"We have to understand in these types of games and stages we have to be smart enough and manage the game better. Everyone has to step up and take responsibility of their own mistakes. Now we don't depend on ourselves but it is what it is."