"He has amazing potential," the Spain international told Arsenal Player.
"I did not know him well when I arrived because he was not at the training sessions due to his injury, and everyone was already talking about him, saying that when he returned, the team would improve, and that has been the case.
"Every day he is gaining more confidence, he is forgetting about the injury, and he is a key player that can influence the result in a game, and thus, we are all very happy to see him 100 per cent again.
"He was out for a long time and it was an injury that takes time to heal.
"It is always hard to come back from injury, especially if it is very long.
"You always have that fear up until you start getting your confidence back, and you start getting back to your old self, and he has done that quickly."