Di Matteo says they are keeping close tabs on him as he begins his second season on loan in Madrid and believes he will soon be ready to challenge Cech.
Di Matteo said: "We follow his progress very closely and have seen him play often, a lot last season.
"He had a very good season over there. He's a very good goalkeeper, despite his young age.
"He's established himself over there and has a lot of people following him in Europe as well as Spain. We are lucky enough to have signed him at the right time. He will spend another year with Atletico Madrid and then we will review his situation.
"He's a top, top goalkeeper. He has all the ability and the potential to become the future of Chelsea."