The Greek has joined on-loan from Wolfsburg.
"I am very happy to be here at Sunderland, which I know is a very good club with a very good coach," he told SAFC TV.
"I am very excited; very happy. The team is good and I believe we can finish in the top eight of the league.
"Plus the club is still competing in the FA Cup - I also hope we can reach the final of the competition."