In the press conference the boss was asked whether Mendy would be fit to return for the Manchester derby, to which Pep replied: "I don't know, I can't anticipate it".
"It's so important for him", Guardiola said of the goal.
Sterling has found the net 19 times this season in the Premier League and Europe, also providing seven assists to prove his elevating performance.
It is barely a year since the winger's future at the Etihad appeared to be in doubt, but Guardiola is aware Sterling's transformation this season into both a goalscorer and effective attacking threat will not have gone unnoticed.
The Spanish coach's system suits the 23-year-old, and his overall philosophy has scaffolded the attacking instincts of all of his flair players.
"In terms of contracts I'm not the guy, it's Txiki [Begiristain, the director of football] that is talking about that".
He may choose to rest Aguero for the game at Goodison Park ahead of the Champions League clash at Liverpool and opt for Gabriel Jesus, who scored the only goal in Brazil's victory over Germany on Tuesday. "The problem with Sergio is he is so important for us". City will be without defender John Stones, who came off during England's 1-1 draw against Italy. "There is no doubt we have to keep him". "But I have still tried to prepare for Everton as if it is the most important game of the season". Of course if it's not going well and we are not winning, you think, 'What do we have to do?' That is normal.
He had said: "In Madrid, I don't have the confidence a player needs".