De Gea continues to be linked with Real Madrid ahead of the summer market.
And asked by El Mundo Deportivo about his teammate's plans, Mata replied: "Will De Gea play at Old Trafford next season? I am not diviner. Nobody knows.
"He is happy, calm and I imagine that he does not think about that for a second, only in the present."
Mata and De Gea are in Spain today for their Champions League clash at Sevilla.