Mourinho is under increased pressure, after picking up three points from 12 in the Premier League and elimination from the FA Cup at Everton this week.
Both managers clash on Saturday at the Etihad Stadium.
Victory for City will keep them on course for a third title in four years, while defeat would pile more pressure on Mourinho, just 15 months into his reign.
Guardiola has now said the high demand for success in England, means managers who fail to win will eventually be shown the door by clubs.
He said: “There’s pressure every day on the manager’s shoulders. We are in a weak position, we have to prove it every day. That is why it’s fascinating.
“You have to be scared to lose, have warnings. Enjoy it the day after or the night if you win, then be thinking about the next one.
“It’s the only way to survive in this business.
“If not, you will be relegated [sacked], for sure.”