Barca's title hopes were further dented on Sunday by defeat at Osasuna.
"Now that it appears as though the league is difficult [to win], it seems as though we are obligated to win the Champions League. As if that were easy. It's not. The challenge is to compete and at the end of the season we'll see where we are," said Guardiola.
"We have to take this one step at a time, because winning the Champions League is a serious challenge. I will not promise that we'll win it. We didn't promise that in the first year, when we were nobodies, and we won't promise to win the title now."