quickly changed his tune on after the forward scored the decisive goal in Sunday's 2-1 victory against Nantes. Greenwood responded to his meagre performance in last month's damaging defeat at home to Paris Saint-Germain with a match-winning contribution at Stade de la Beaujoire.
Marseille had suffered a 3-0 humbling on home turf at the hands of PSG in their previous Ligue 1 outing, widening the gap at the table summit to six points.
Greenwood endured a dismal first half and was hauled off at half-time by De Zerbi, who didn't shy away from criticising the former Manchester United star.
When explaining the reason for the brutal substitution, De Zerbi said: "Because I didn't like the way he played. If we want to compete for the title we have to push in all matches.
"I think he was having a bad day. He [has given] us a lot of goals and points, but when you're at Olympique Marseille, if you want to fight for the championship, you have to push in every match.
"You can't say you're [producing] a good performance by scoring two goals and then having a bad patch the next match. It's not possible.
"He's a good player, but I expected more from him tonight. But not only from him. I always expect more in general."
Against Nantes, Neal Maupay had struck Marseille into the lead just before the half-hour mark before the hosts drew level through Tino Kadewere later in the first half.
Greenwood fired De Zerbi's side back into the lead with an effort from the edge of the area on 61 minutes and earned praise from his manager after full-time.
In sharp contrast to his criticism of the 23-year-old a week earlier, the Italian coach stated: "First of all, he's a great guy.
"He's very committed and always gives everything he has. He's a very strong player, and he makes the difference for Olympique Marseille.
"I was surprised by Greenwood last week because he didn't play well [in the 3-0 loss to PSG]. He was far from his standards. Tonight, I wasn't surprised by Greenwood."
The ex-United No. 11 has enjoyed an impressive start to life in Marseille, scoring seven goals and registering two assists in 10 appearances.
He produced 10 goals and six assists in 36 games on loan at Getafe last season before completing a £30million switch to France.
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