City have a buy-back option set at around £25million for the Brazilian, 22, they sold two years ago.
Guardiola said: “There are a lot of people at the club working about these kind of players and at the end of the season we are going to take a decision.
“I have many things in my head for these five or six weeks. All of us have.
“We've fought a lot to be here, to be in the Champions League semi final for only the second time."
Guardiola did admit he was impressed by what he has seen of Luiz and with his performance in City's 2-1 win at Villa Park on Wednesday night.
He said: “He's played a lot of minutes, important for Villa. A guy who is clever with the ball, physically strong. A lovely guy.
“Unfortunately he could not play with us because of the work permit but he is developing really well and I'm happy for him.
“Today when he was involved in the game both defensively and offensively he was good."