RB Leipzig has ruled out Dayot Upamecano leaving this season.
The 21-year-old has been linked strongly with a move to Manchester United after admitting he was speaking other clubs.
But while Nagelsmann will keep hold of the centre-back, the German said it was likely he could leave next summer.
"He [Upamecano] will be here for the season. I'm sure about that," the Leipzig manager told ESPN. "As for the future, I'm not sure as he is very talented.
"Lots of clubs will want to buy - next season it could be real that he leaves the club. But this season he will stay."
