The 30-year-old has been in excellent form since his move last summer, featuring in all seven matches for the Toffees this season, scoring one goal and providing four assists.
His exploits with Everton under David Moyes leadership were immediately rewarded with the Premier League Player of the Month award for August and he has continued to impress, scoring the winner to end Crystal Palace unbeaten run recently.
"The important thing is he is back," said Guardiola.
"He is a massive influence in the Everton games. After what's happened, maybe Manchester City want him back, but I don't know. Many things are still going to happen. We'll see.
"The important thing is he is playing again, a lot of minutes. This is the standard. I'm happy, really, honestly, that he's back in, trying his best."
However, Grealish will miss this weekend's Premier League clash against Manchester City due the FA's rules which prevent loaned players from facing their parent clubs during the duration of their loan.
Everton are eighth on the Premier League table and would go above Manchester City in fifth position if they can win at the Etihad Stadium this Saturday.
Ange Postecoglou's nightmare start at Nottingham Forest continued as his side were comfortably beaten 3-0 by Chelsea at the City Ground, extending their winless run to eight Premier League matches.
Ange Postecoglou's turbulent spell as Nottingham Forest manager has come to an abrupt end after just 39 days in charge, following Saturday's 3-0 defeat to Chelsea at the City Ground.
Tottenham Hotspur manager Thomas Frank has confirmed that striker Randal Kolo Muani is close to full fitness and could feature against Aston Villa on Sunday at the Tottenham Hotspur Stadium.
Crystal Palace captain Marc Guehi has informed the club that he will not extend his contract and plans to leave next summer, manager Oliver Glasner confirmed on Friday.
