The former Manchester United forward has just committed his international future to Jamaica and has scored 16 goals in 27 appearances this season.
However, OM coach De Zerbi dropped him to the bench for the clash with Lens, which the hosts lost 1-0. Greenwood was thrown on at halftime at the Velodrome, but couldn't make a difference.
De Zerbi said of his decision: "No one can have more respect for him (Greenwood) than I do.
"But that doesn't change anything: I expect more from him. He has to do more, because what he is currently showing is not enough.
"If he wants to achieve his ambition of becoming a champion, he has to be more consistent, sacrifice more and be more determined.
"Otherwise, we as a team always fall back into the same pattern: a very good match, then a defeat at Auxerre, then a victory against Nantes… It's too irregular, it's like waves. And that's something I don't like."