City go into the Champions League Round of 16 second leg against the Portuguese with a commanding 5-0 lead from the first tie in Lisbon.
But Guardiola insists anything other than full concentration from his players and the complexion of the match could change quickly.
“We will be in trouble if they are not (fully focused),” said Pep.
“It’s our job and our duty. We have to do it. Once we are there we can try to do well or do it wrong, it’s the same price, no discounts.
“Do what you can. Try. I am not asking to perform like we did against United for example in the second half.
“Football is not like this - but try - that is all.”
The boss was also asked for his thoughts on the fact his team had spread goals around more than any side left in the competition with 10 different scorers to date.
“We played with a number nine, but when teams press high, maybe drop in you can find spaces,” he said.
“When a team defends so deep and doesn’t move you don’t need a false nine, you need a striker but we don’t have it.
“We have Gabriel, but he likes to move more in the sides.
“From day one we want everyone involved in the process to defend and attack and they have permission to arrive in the box.
“Why did Kevin score two last game? Because he was there. Why score the first goal in Portugal when cross hit the post, deflection, Kevin passed to Riyad? He was there.
“To score goals you have to be there. How we arrive as many players after a lot of passes, they don’t lose stupid balls to counters and with a lot of passes we arrive.
“We make good transitions, Bernardo can’t make 40-50 metre transitions, Leroy (Sane) could do it, Raheem Sterling can do it, Sam Edozie can do it, but the rest, Riyad can’t do it.
“We need to go with the ball and when this happens, we arrive with four or five players in the box and we can score otherwise we struggle a lot.”
