"I felt that, against Platanias, whenever they needed to up their game they could step up a gear.
"What we did see, though, was that Olympiacos were non-physical. They weren't interested in closing the other team down quickly – they allowed them plenty of time on the ball."
David Moyes' side meet Olympiacos in Athens for the Champions League last 16 first leg on Tuesday 25 February.
Following that tie, United supporters will be able to watch the Athens derby, against Panathinaikos, live on MUTV on Sunday 2 March (kick-off 17:30 GMT) before the Reds and Olympiacos meet at Old Trafford on 19 March.
More: Watch Olympiacos on MUTV