The Premier League giants are set to take on Panathinaikos in the group stages on Thursday.
While Maresca knows his team are favorites going into the game, he is aware of the challenge they will face.
On his memories of Pana from his time at Olympiacos, he stated: "Many years ago, the feeling is a little bit mixed in terms of the season I spent here in Greece, for me it was very good with Olympiacos, big rival with Panathinaikos but at the same time I was here in Greece, unfortunately I lost a friend on the pitch when I was at Seville and the first game we played after that, we were already here in Athens, just in that day, one of our teammates passed away in Antonio Puerta.
"So it is a bit mixed feeling. The season in Athens was fantastic but every time I come back here, I am a little bit sad."
He added on their strengths: "As I said, Panathinaikos have some good players.
“For instance, I was at Leicester last year, Tete was there two years ago, so I know something. They have different types of players. Also, the manager was in Seville.
"Overall, like all the clubs, they have good things and some problems. We are going to do our best and to compete in the right way tomorrow."