City were defeated 3-2 at home in the first leg of their play-off clash last week despite leading 2-1 with just four minutes left in the tie.
"The margin to win at the Bernabeu from that position, everybody knows, the percentage to go through, we arrive at one per cent. Or I don't know what, but it will be minimal," said Guardiola.
"But as much as you have a chance we will try, that's for sure. We are going like we always have done but, this season, the reality is we have been miles away.
"We have been really, really poor in performances and results this season."
City go to Spain buoyed by a 4-0 win over Newcastle in the Premier League which kept them on course for a return to the Champions League even if this season's campaign ends on Wednesday.
"For one game, Saturday, we played really good but it's not going to change the opinion, the reality. But, of course, it's better to travel to Madrid with this result," added the City manager.