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.
Manchester City secured a second successive Premier League victory at home against Sunderland, Chelsea were held scoreless away to Bournemouth while Tottenham managed to beat Brentford.
Aston Villa delivered a major jolt to the Premier League title race as Emiliano Buendía struck deep into stoppage time to seal a 2-1 win over Arsenal on Saturday.
David Moyes urged Everton to stay on the front foot as they prepare for Saturday's Premier League meeting with Nottingham Forest at Hill Dickinson Stadium, where Sean Dyche made his first return since leaving the club nearly a year ago.
Mikel Arteta has said that Aston Villa's blistering run of form has made them genuine contenders in the Premier League title race, as Arsenal prepare for a high-stakes trip to Villa Park.
