Real Madrid paid 60 million euros for his transfer in the summer of 2019, but the Serbian struggled for minutes in the Spanish capital and departed on loan in January.
"I will think about that at the end of the season," he said when his future was brought up in an interview with BILD.
"Right now I'm only thinking about Eintracht Frankfurt and I'm working to be able to play as well as possible in the upcoming games.
"Anything is possible because you never know what will happen in professional football.
"Coming back [on loan] was the right decision because a lot of things fit for me here.
"But, most important is the success of the team. If the team is doing well then that's positive for me.
"Each win for the team is a step forward for me. Of course, I want to play my part and help the team."