The Blaugrana qualified for the group stages of the Champions League group stage after winning the first leg against the Poles, but they were beaten on Tuesday night thanks to a goal from Cléber.
After the game Guardiola was not upset as Wisla became the first ever Polish team to beat Barça and believes that his players had done enough to take something from the match.
"I do not believe that we have taken a step back in our preparations. We have not been as good as we should have been, but the opposition also played well and we had five or six chances," he told reporters.
"We have lost, but we could have drawn or even won the game. I am pleased that we have qualified because I have seen a lot of ties like this that have ended up being very close."
On Sunday, Barcelona open their league account with a trip to Numancia and Guardiola recognised that it will not be an easy encounter to start the season.
"I know that going to play the teams that have just come up will be difficult," he added.