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.
Mikel Arteta has described Granit Xhaka as "one of the signings of the season" ahead of Arsenal's reunion with their former midfielder when they face Sunderland at the Stadium of Light on Saturday.
Strasbourg's on-loan defender Mamadou Sarr has chosen to represent Senegal at international level despite having represented multiple France youth teams.
Jadon Sancho's struggles deepened on Thursday night as the on-loan Manchester United winger failed to seize his opportunity in Aston Villa's 2-0 victory over Maccabi Tel Aviv.
Oliver Glasner has praised Crystal Palace's fighting spirit but admitted his side "still have plenty to improve" despite a commanding 3-1 home victory over AZ Alkmaar in the UEFA Conference League.
