The striker was an admirer of the Armenian's talents before he joined the Serie A side and has been impressed so far.
He told Sky Sports: "I expect it from him. I know him as a great player, and he is a very good addition to our attacking team who wants to play football.
"He's a great pro. I remember him also from Borussia Dortmund times and he will be a big player for us. Hopefully, he can stay a long time here.
"Hopefully he will [stay]. He will see that we are playing football here and immediately he scored a goal, so hopefully he can have more goals and a lot of assists for us."