Based on the fact he has spent the last 6 seasons playing in the Greek League?
He has a great scoring record in the Greek League…. But then Ruiz had a great scoring record in the Dutch League
I think it's difficult to judge whether a player will be good in the PL on the amount of goals they've scored in another league. You're better off looking at the player's strengths and weaknesses. Ruiz is lightweight and needs time on the ball, isn't an out and out striker. Mitroglou is fast, strong, tall and a decent finisher. That sounds a lot more like a Premier League player to me. Only time will tell of course but I'm optimistic.
