The Serb joined Real last summer from Eintracht Frankfurt, but has struggled for form and fitness in his first season in Spain.
Berbatov says: "We Balkans sometimes do things differently, but I hope he can focus on what is really important to him: getting fit and showing that Real Madrid was right when they paid what they paid for his transfer.
"It is true that he may not reach the end of the season and that he has had bad luck with the injuries. Also that he has not been able to demonstrate what was seen of him at Eintracht in Frankfurt when he left.
"But I insist that he is an investment for the future. He is going through a difficult situation because he is injured and that, mentally, will be hard, but he has to think positive and project himself on how he will play good games for next season."