The Arsenal midfielder will face City with Bournemouth today.
Guardiola said: "When I was the coach of Barcelona, he made his debut at 18. He was so young.
"I said: 'Wow. This player is really good'. Unfortunately, he suffered a lot of injuries. I wish him the best.
"I hope he can play regularly for Bournemouth and not suffer more injuries. He is a special player in the way he can attack a central defender."