"You can't imagine how different it is playing with people than without people," said Guardiola.
"It doesn't compare. In the end we played behind closed doors so the economy of world football would survive, for the broadcasters. Thanks to that, we kept getting our salaries and could play football for the people.
"Hopefully it won't happen again, but cases are raised all around the world. These people go to the stadiums, and can contaminate.
"There are people in the stadiums who don't use masks, and that surprises me the most. You walk in the street, you go to the big malls, to places to buy presents for the family and no one uses masks.
"Vaccinations, booster jabs, the people [can] decide, but a part of that has to be social distancing and masks. It's the best way to protect ourselves, our families and the rest of the people.
"Like this, the restaurants could still be open, and football could go on. I'm not a scientist or a doctor but I trust the doctors and scientists because they know more than I know.
"Wearing a mask is so important, like social distancing and hand sanitisers, so let's try to do it. Otherwise, it may [come back] again and again and again."