Paul Pogba has been urged to "show up" for Manchester United and prove what he is capable of as he nears the end of his Old Trafford contract.
The 28-year-old is set to return to United's squad for Friday's FA Cup fourth-round tie against Middlesbrough after three months out with a thigh injury.
France international Pogba has just four months remaining on his deal with the Red Devils and is now widely expected to seek a new challenge at the end of the campaign.
Regardless of where Pogba intends to play his football beyond this season, Rangnick simply wants the central midfielder to be fully motivated in order to find his best form.
"It's up to him now. His contract is expiring in the summer and if in the end he would like to stay or go somewhere else he has to show up," Rangnick said.
"It's not only in the interest for us as a club but it's in his personal interest that he plays and performs at the highest possible level in the next couple of weeks."
Pogba remains United's record signing, having rejoined from Juventus in 2016 for an initial fee of £89.3million (€105m), but the Red Devils now stand to lose him for nothing.
He has made 212 appearances in his second spell at Old Trafford, during which time he has scored 38 goals and assisted 45 more in all competitions.
While a new deal has not entirely been ruled out for the Real Madrid, Barcelona, Paris Saint-Germain and Juve target, Rangnick is only focused on the remainder of 2021-22.
"We haven't spoken about it so far, not only about Paul's situation but also with other contracts expiring we also didn't speak about new players so far," Rangnick said.
"My focus now is to play the best possible season we can and to be as successful as we can be.
"For me he is now a new player and he can show me and the team and the fans and everyone in England how good and what high level he can play."
Prior to sustaining his injury, Pogba led the way in the Premier League for assists with seven from nine appearances, averaging exactly one assist per 90 minutes on the pitch.
Despite him missing United's last 15 matches, only Bruno Fernandes (10) has assisted more goals than Pogba (seven) for the Red Devils in all competitions this season.
However, Rangnick insisted the World Cup-winning midfielder is not assured of a starting place in the team.
"For Paul it is in his own interest to play on a high level to have a good performance and do everything to get into the first XI – that will not automatically happen," Rangnick said.
United host Middlesbrough aiming to build on a record of 28 wins from their last 31 home FA Cup matches against sides from a lower division.