The Czech Republic international moved across town in a £10million deal ending an 11-year association with Chelsea earlier this summer and Matic suggests the Gunners will get plenty out of the 33-year-old.
"Petr is a great guy and a great keeper," Matic said. "It is going to be a very important signing for them.
"But I am not happy because of that. We know that he is very professional.
"He is one of the best keepers. And I hope this season he does not perform as he did here for 10-11 years.
"I am happy for him because he gets to stay in London, which for him and his family was very important. I wish him all the best."