The Argentinian has not played for Spurs since October.
Pochettino said: "Now we start to be concerned about him because he is three months and still in a situation that has not moved on.
"Tomorrow he will have a scan. Still it is difficult to give the time that he can come back. We need to wait tomorrow because there is still some problems, and we are still not sure of the diagnosis."
The Spurs boss added: "First of all, the injury was nothing. Then, it was a little bit and then, it was that minor problem still, still, still, every day.
"Then, he had the problem with his brother. He went to Argentina. Stop. Then he came back and that affected a little bit his mind and now he was recovering very slowly. And it's for that, he is very anxious."